Descent of Man [ 1871]

[Bullseye]

* See also Mr. Bates's paper in Proc. Ent. Soc. of Philadelphia,
1865, p. 206. Also Mr. Wallace on the same subject, in regard to
Diadema, in Transactions, Entomological Society, London, 1869, p. 278.

  In the genus Papilio, all the species of the Aeneas group are
remarkable for their conspicuous and strongly contrasted colours,
and they illustrate the frequent tendency to gradation in the amount
of difference between the sexes. In a few species, for instance in
P. ascanius, the males and females are alike; in others the males
are either a little brighter, or very much more superb than the
females. The genus Junonia, allied to our Vanessae, offers a nearly
parallel case, for although the sexes of most of the species
resemble each other, and are destitute of rich colours, yet in certain
species, as in J. oenone, the male is rather more bright-coloured than
the female, and in a few (for instance J. andremiaja) the male is so
different from the female that he might be mistaken for an entirely
distinct species.
  Another striking case was pointed out to me in the British Museum by
Mr. A. Butler, namely, one of the tropical American Theclae, in
which both sexes are nearly alike and wonderfully splendid; in another
species the male is coloured in a similarly gorgeous manner, whilst
the whole upper surface of the female is of a dull uniform brown.
Our common little English blue butterflies of the genus Lycaena,
illustrate the various differences in colour between the sexes, almost
as well, though not in so striking a manner, as the above exotic
genera. In Lycaena agestis both sexes have wings of a brown colour,
bordered with small ocellated orange spots, and are thus alike. In
L. oegon the wings of the males are of a fine blue, bordered with
black, whilst those of the female are brown, with a similar border,
closely resembling the wings of L. agestis. Lastly, in L. arion both
sexes are of a blue colour and are very like, though in the female the
edges of the wings are rather duskier, with the black spots plainer;
and in a bright blue Indian species both sexes are still more alike.
  I have given the foregoing details in order to show, in the first
place, that when the sexes of butterflies differ, the male as a
general rule is the more beautiful, and departs more from the usual
type of colouring of the group to which the species belongs. Hence
in most groups the females of the several species resemble each
other much more closely than do the males. In some cases, however,
to which I shall hereafter allude, the females are coloured more
splendidly than the males. In the second place, these details have
been given to bring clearly before the mind that within the same
genus, the two sexes frequently present every gradation from no
difference in colour, to so great a difference that it was long before
the two were placed by entomologists in the same genus. In the third
place, we have seen that when the sexes nearly resemble each other,
this appears due either to the male having transferred his colours
to the female, or to the male having retained, or perhaps recovered,
the primordial colours of the group. It also deserves notice that in
those groups in which the sexes differ, the females usually somewhat
resemble the males, so that when the males are beautiful to an
extraordinary degree, the females almost invariably exhibit some
degree of beauty. From the many cases of gradation in the amount of
difference between the sexes, and from the prevalence of the same
general type of coloration throughout the whole of the same group,
we may conclude that the causes have generally been the same which
have determined the brilliant colouring of the males alone of some
species, and of both sexes of other species.
  As so many gorgeous butterflies inhabit the tropics, it has often
been supposed that they owe their colours to the great heat and
moisture of these zones; but Mr. Bates* has shown by the comparison of
various closely-allied groups of insects from the temperate and
tropical regions, that this view cannot be maintained; and the
evidence becomes conclusive when brilliantly-coloured males and
plain-coloured females of the same species inhabit the same
district, feed on the same food, and follow exactly the same habits of
life. Even when the sexes resemble each other, we can hardly believe
that their brilliant and beautifully arranged colours are the
purposeless result of the nature of the tissues and of the action of
the surrounding conditions.

  * The Naturalist on the Amazons, vol. i., 1863, p. 19.

  With animals of all kinds, whenever colour has been modified for
some special purpose, this has been, as far as we can judge, either
for direct or indirect protection, or as an attraction between the
sexes. With many species of butterflies the upper surfaces of the
wings are obscure; and this in all probability leads to their escaping
observation and danger. But butterflies would be particularly liable
to be attacked by their enemies when at rest; and most kinds whilst
resting raise their wings vertically over their backs, so that the
lower surface alone is exposed to view. Hence it is this side which is
often coloured so as to imitate the objects on which these insects
commonly rest. Dr. Rossler, I believe, first noticed the similarity of
the closed wings of certain Vanessae and other butterflies to the bark
of trees. Many analogous and striking facts could be given. The most
interesting one is that recorded by Mr. Wallace* of a common Indian
and Sumatran butterfly (Kallima) which disappears like magic when it
settles on a bush; for it hides its head and antennae between its
closed wings, which, in form, colour and veining, cannot be
distinguished from a withered leaf with its footstalk. In some other
cases the lower surfaces of the wings are brilliantly coloured, and
yet are protective; thus in Thecla rubi the wings when closed are of
an emerald green, and resemble the young leaves of the bramble, on
which in spring this butterfly may often be seen seated. It is also
remarkable that in very many species in which the sexes differ greatly
in colour on their upper surface, the lower surface is closely similar
or identical in both sexes, and serves as a protection.*(2)

  * See the interesting article in the Westminster Review, July, 1867,
p. 10. A woodcut of the Kallima is given by Mr. Wallace in Hardwicke's
Science Gossip, September 1867, p. 196.
  *(2) Mr. G. Fraser, in Nature, April, 1871, p. 489.

[Bullseye]

Although the obscure tints both of the upper and under sides of many
butterflies no doubt serve to conceal them, yet we cannot extend
this view to the brilliant and conspicuous colours on the upper
surface of such species as our admiral and peacock Vanessae, our white
cabbage-butterflies (Pieris), or the great swallowtail Papilio which
haunts the open fens- for these butterflies are thus rendered
visible to every living creature. In these species both sexes are
alike; but in the common brimstone butterfly (Gonepteryx rhamni),
the male is of an intense yellow, whilst the female is much paler; and
in the orange-tip (Anthocharis cardamines) the males alone have
their wings tipped with bright orange. Both the males and females in
these cases are conspicuous, and it is not credible that their
difference in colour should stand in any relation to ordinary
protection. Prof. Weismann remarks,* that the female of one of the
Lycaenae expands her brow wings when she settles on the ground, and is
then almost invisible; the male, on the other hand, as if aware of the
danger incurred from the bright blue of the upper surface of his
wings, rests with them closed; and this shows that the blue colour
cannot be in any way protective. Nevertheless, it is probable that
conspicuous colours are indirectly beneficial to many species, as a
warning that they are unpalatable. For in certain other cases,
beauty has been gained through the imitation of other beautiful
species, which inhabit the same district and enjoy an immunity from
attack by being in some way offensive to their enemies; but then we
have to account for the beauty of the imitated species.

  * Einfluss der Isolirung auf die Artbildung, 1872, p. 58.

  As Mr. Walsh has remarked to me, the females of our orange-tip
butterfly, above referred to, and of an American species (Anth.
genutia) probably show us the primordial colours of the parent-species
of the genus; for both sexes of four or five widely-distributed
species are coloured in nearly the same manner. As in several previous
cases, we may here infer that it is the males of Anth. cardamines
and genutia which have departed from the usual type of the genus. In
the Anth. sara from California, the orange-tips to the wings have been
partially developed in the female; but they are paler than in the
male, and slightly different in some other respects. In an allied
Indian form, the Iphias glaucippe, the orange-tips are fully developed
in both sexes. In this Iphias, as pointed out to me by Mr. A.
Butler, the under surface of the wings marvellously resembles a
pale-coloured leaf; and in our English orange-tip, the under surface
resembles the flower-head of the wild parsley, on which the
butterfly often rests at night.* The same reason which compels us to
believe that the lower surfaces have here been coloured for the sake
of protection, leads us to deny that the wings have been tipped with
bright orange for the same purpose, especially when this character
is confined to the males.

  * See the interesting observations by T. W. Wood, the Student,
Sept., 1868, p. 81.

  Most moths rest motionless during the whole or greater part of the
day with their wings depressed; and the whole upper surface shaded and
coloured in an admirable manner, as Mr. Wallace has remarked, for
escaping detection. The front-wings of the Bombycidae,* when at
rest, generally overlap and conceal the hind-wings; so that the latter
might be brightly coloured without much risk; and they are in fact
often thus coloured. During flight, moths would often be able to
escape from their enemies; nevertheless, as the hind-wings are then
fully exposed to view, their bright must generally have been
acquired at some little risk. But the following fact shews how
cautious we ought to be in drawing conclusions on this head. The
common yellow under-wings (Triphoena) often fly about during the day
or early evening, and are then conspicuous from the colour of their
hind-wings. It would naturally be thought that this would be a
source of danger; but Mr. J. Jenner Weir believes that it actually
serves them as a means of escape, for birds strike at these brightly
coloured and fragile surfaces, instead of at the body. For instance,
Mr. Weir turned into his aviary a vigorous specimen of Triphoena
pronuba, which was instantly pursued by a robin; but the bird's
attention being caught by the coloured wings, the moth was not
captured until after about fifty attempts, and small portions of the
wings were repeatedly broken off. He tried the same experiment, in the
open air, with a swallow and T. fimbria; but the large size of this
moth probably interfered with its capture.*(2) We are thus reminded of
a statement made by Mr. Wallace,*(3) namely, that in the Brazilian
forests and Malayan islands, many common and highly-decorated
butterflies are weak flyers, though furnished with a broad expanse
of wing; and they "are often captured with pierced and broken wings,
as if they had been seized by birds, from which they had escaped: if
the wings had been much smaller in proportion to the body, it seems
probable that the insect would more frequently have been struck or
pierced in a vital part, and thus the increased expanse of the wings
may have been indirectly beneficial."

[Bullseye]

* Mr. Wallace in Harwicke's Science Gossip, September, 1867, p. 193.
  *(2) See also, on this subject, Mr. Weir's paper in Transactions,
Entomological Society, 1869, p. 23.
  *(3) Westminster Review, July, 1867, p. 16.

  Display.- The bright colours of many butterflies and of some moths
are specially arranged for display, so that they may be readily
seen. During the night colours are not visible, and there can be no
doubt that the nocturnal moths, taken as a body, are much less gaily
decorated than butterflies, all of which are diurnal in their
habits. But the moths of certain families, such as the Zygaenidae,
several Sphingidae, Uraniidae, some Arctiidae and Saturniidae, fly
about during the day or early evening, and many of these are extremely
beautiful, being far brighter coloured than the strictly nocturnal
kinds. A few exceptional cases, however, of bright-coloured
nocturnal species have been recorded.*

  * For instance, Lithosia; but Prof. Westwood (Modern Class. of
Insects, vol. ii., p. 390) seems surprised at this case. On the
relative colours of diurnal and nocturnal Lepidoptera, see ibid.,
pp. 333 and 392; also Harris, Treatise on the Insects of New
England, 1842, p. 315.

  There is evidence of another kind in regard to display. Butterflies,
as before remarked, elevate their wings when at rest, but whilst
basking in the sunshine often alternately raise and depress them, thus
exposing both surfaces to full view; and although the lower surface is
often coloured in an obscure manner as a protection, yet in many
species it is as highly decorated as the upper surface, and
sometimes in a very different manner. In some tropical species the
lower surface is even more brilliantly coloured than the upper.* In
the English fritillaries (Argynnis) the lower surface alone is
ornamented with shining silver. Nevertheless, as a general rule, the
upper surface, which is probably more fully exposed, is coloured
more brightly and diversely than the lower. Hence the lower surface
generally affords to entomologists the more useful character for
detecting the affinities of the various species. Fritz Muller
informs me that three species of Castnia are found near his house in
S. Brazil: of two of them the hind-wings are obscure, and are always
covered by the front-wings when these butterflies are at rest; but the
third species has black hind-wings, beautifully spotted with red and
white, and these are fully expanded and displayed whenever the
butterfly rests. Other such cases could be added.

  * Such differences between the upper and lower surfaces of the wings
of several species of Papilio may be seen in the beautiful plates to
Mr. Wallace's "Memoir on the Papilionidae of the Malayan Region," in
Transactions of the Linnean Society, vol. xxv., part i., 1865.

  If we now turn to the enormous group of moths, which, as I hear from
Mr. Stainton, do not habitually expose the under surface of their
wings to full view, we find this side very rarely coloured with a
brightness greater than, or even equal to, that of the upper side.
Some exceptions to the rule, either real or apparent, must be noticed,
as the case of Hypopyra.* Mr. Trimen informs me that in Guenee's great
work, three moths are figured, in which the under surface is much
the more brilliant. For instance, in the Australian Gastrophora the
upper surface of the fore -wing is pale greyish-ochreous, while the
lower surface is magnificently ornamented by an ocellus of
cobalt-blue, placed in the midst of a black mark, surrounded by
orange-yellow, and this by bluish-white. But the habits of these three
moths are unknown; so that no explanation can be given of their
unusual style of colouring. Mr. Trimen also informs me that the
lower surface of the wings in certain other Geometrae*(2) and
quadrifid Noctuae are either more variegated or more brightly-coloured
than the upper surface; but some of these species have the habit of
"holding their wings quite erect over their backs, retaining them in
this position for a considerable time," and thus exposing the under
surface to view. Other species, when settled on the ground or herbage,
now and then suddenly and slightly lift up their wings. Hence the
lower surface of the wings being brighter than the upper surface in
certain moths is not so anomalous as it at first appears. The
Saturniidae include some of the most beautiful of all moths, their
wings being decorated, as in our British emperor moth, with fine
ocelli; and Mr. T. W. Wood*(3) observes that they resemble butterflies
in some of their movements; "for instance, in the gentle waving up and
down of the wings as if for display, which is more characteristic of
diurnal than of nocturnal Lepidoptera."

  * See Mr. Wormald on this moth: Proceedings of the Entomological
Society, March 2, 1868.
  *(2) See also an account of the S. American genus Erateina (one of
the Geometrae) in Transactions, Ent., Soc., new series, vol. v.,
pls. xv. and xvi.
  *(3) Proc Ent. Soc. of London, July 6, 1868, p. xxvii.

  It is a singular fact that no British moths which are brilliantly
coloured, and, as far as I can discover, hardly any foreign species,
differ much in colour according to sex; though this is the case with
many brilliant butterflies. The male, however, of one American moth,
the Saturnia io, is described as having its forewings deep yellow,
curiously marked with purplish-red spots; whilst the wings of the
female are purple-brown, marked with grey lines.* The British moths
which differ sexually in colour are all brown, or of various dull
yellow tints, or nearly white. In several species the males are much
darker than the females,*(2) and these belong to groups which
generally fly about during the afternoon. On the other hand, in many
genera, as Mr. Stainton informs me, the males have the hind-wings
whiter than those of the female- of which fact Agrotis exclamationis
offers a good instance. In the ghost-moth (Hepialus humuli) the
difference is more strongly marked; the males being white, and the
females yellow with darker markings.*(3) It is probable that in
these cases the males are thus rendered more conspicuous, and more
easily seen by the females whilst flying about in the dusk.

  * Harris, Treatise, &c., edited by Flint, 1862, p. 395.
  *(2) For instance, I observe in my son's cabinet that the males
are darker than the females in the Lasiocampa quercus Odonestis
potatoria, Hypogymna dispar, Dasychira pudibunda, and Cycnia
mendica. In this latter species the difference in colour between the
two sexes is strongly marked; and Mr. Wallace informs me that we
here have, as he believes, an instance of protective mimicry
confined to one sex, as will hereafter be more fully explained. The
white female of the Cycnia resembles the very common Spilosoma
menthrasti, both sexes of which are white; and Mr. Stainton observed
that this latter moth was rejected with utter disgust by a whole brood
of young turkeys, which were fond of eating other moths; so that if
the Cycnia was commonly mistaken by British birds for the Spilosoma,
it would escape being devoured, and its white deceptive colour would
thus be highly beneficial.
  *(3) It is remarkable, that in the Shetland Islands the male of this
moth, instead of differing widely from the female, frequently
resembles her closely in colour (see Mr. MacLachlan, Transactions,
Entomological Society, vol. ii., 1866, p. 459). Mr. G. Fraser suggests
(Nature, April, 1871, p. 489) that at the season of the year when
the ghost-moth appears in these northern islands, the whiteness of the
males would not be needed to render them visible to the females in the
twilight night.

[Bullseye]

From the several foregoing facts it is impossible to admit that
the brilliant colours of butterflies, and of some few moths, have
commonly been acquired for the sake of protection. We have seen that
their colours and elegant patterns are arranged and exhibited as if
for display. Hence I am led to believe that the females prefer or
are most excited by the more brilliant males; for on any other
supposition the males would, as far as we can see, be ornamented to no
purpose. We know that ants and certain lamellicorn beetles are capable
of feeling an attachment for each other, and that ants recognise their
fellows after an interval of several months. Hence there is no
abstract improbability in the Lepidoptera, which probably stand nearly
or quite as high in the scale as these insects, having sufficient
mental capacity to admire bright colours. They certainly discover
flowers by colour. The humming-bird sphinx may often be seen to
swoop down from a distance on a bunch of flowers in the midst of green
foliage; and I have been assured by two persons abroad, that these
moths repeatedly visit flowers painted on the walls of a room, and
vainly endeavour to insert their proboscis into them. Fritz Muller
informs me that several kinds of butterflies in S. Brazil shew an
unmistakable preference for certain colours over others: he observed
that they very often visited the brilliant red flowers of five or
six genera of plants, but never the white or yellow flowering
species of the same and other genera, growing in the same garden;
and I have received other accounts to the same effect. As I hear
from Mr. Doubleday, the common white butterfly often flies down to a
bit of paper on the ground, no doubt mistaking it for one of its own
species. Mr. Collingwood* in speaking of the difficulty in
collecting certain butterflies in the Malay Archipelago, states that
"a dead specimen pinned upon a conspicuous twig will often arrest an
insect of the same species in its headlong flight, and bring it down
within easy reach of the net, especially if it be of the opposite
sex."

  * Rambles of a Naturalist in the Chinese Seas, 1868, p. 182.

  The courtship of butterflies is, as before remarked, a prolonged
affair. The males sometimes fight together in rivalry; and many may be
seen pursuing or crowding round the same female. Unless, then, the
females prefer one male to another, the pairing must be left to mere
chance, and this does not appear probable. If, on the other band,
the females habitually, or even occasionally, prefer the more
beautiful males, the colours of the latter will have been rendered
brighter by degrees, and will have been transmitted to both sexes or
to one sex, according to the law of inheritance which has prevailed.
The process of sexual selection will have been much facilitated, if
the conclusion can be trusted, arrived at from various kinds of
evidence in the supplement to the ninth chapter; namely, that the
males of many Lepidoptera, at least in the imago state, greatly exceed
the females in number.
  Some facts, however, are opposed to the belief that female
butterflies prefer the more beautiful males; thus, as I have been
assured by several collectors, fresh females may frequently be seen
paired with battered, faded, or dingy males; but this is a
circumstance which could hardly fail often to follow from the males
emerging from their cocoons earlier than the females. With moths of
the family of the Bombycidae, the sexes pair immediately after
assuming the imago state; for they cannot feed, owing to the
rudimentary condition of their mouths. The females, as several
entomologists have remarked to me, lie in an almost torpid state,
and appear not to evince the least choice in regard to their partners.
This is the case with the common silk-moth (B. mori), as I have been
told by some continental and English breeders. Dr. Wallace, who has
had great experience in breeding Bombyx cynthia, is convinced that the
females evince no choice or preference. He has kept above 300 of these
moths together, and has often found the most vigorous females mated
with stunted males. The reverse appears to occur seldom; for, as he
believes, the more vigorous males pass over the weakly females, and
are attracted by those endowed with most vitality. Nevertheless, the
Bombycidae, though obscurely-coloured, are often beautiful to our eyes
from their elegant and mottled shades.
  I have as yet only referred to the species in which the males are
brighter coloured than the females, and I have attributed their beauty
to the females for many generations having chosen and paired with
the more attractive males. But converse cases occur, though rarely, in
which the females are more brilliant than the males; and here, as I
believe, the males have selected the more beautiful females, and
have thus slowly added to their beauty. We do not know why in
various classes of animals the males of some few species have selected
the more beautiful females instead of having gladly accepted any
female, as seems to be the general rule in the animal kingdom: but if,
contrary to what generally occurs with the Lepidoptera, the females
were much more numerous than the males, the latter would be likely
to pick out the more beautiful females. Mr. Butler shewed me several
species of Callidryas in the British Museum, in some of which the
females equalled, and in others greatly surpassed the males in beauty;
for the females alone have the borders of their wings suffused with
crimson and orange, and spotted with black. The plainer males of these
species closely resemble each other, shewing that here the females
have been modified; whereas in those cases, where the males are the
more ornate, it is these which have been modified, the females
remaining closely alike.
  In England we have some analogous cases, though not so marked. The
females alone of two species of Thecla have a bright-purple or
orange patch on their fore-wings. In Hipparchia the sexes do not
differ much; but it is the female of H. janira which has a conspicuous
light-brown patch on her wings; and the females of some of the other
species are brighter coloured than their males. Again, the females
of Colias edusa and hyale have "orange or yellow spots on the black
marginal border, represented in the males only by thin streaks"; and
in Pieris it is the females which "are ornamented with black spots
on the fore-wings, and these are only partially present in the males."
Now the males of many butterflies are known to support the females
during their marriage flight; but in the species just named it is
the females which support the males; so that the part which the two
sexes play is reversed, as is their relative beauty. Throughout the
animal kingdom the males commonly take the more active share in
wooing, and their beauty seems to have been increased by the females
having accepted the more attractive individuals; but with these
butterflies, the females take the more active part in the final
marriage ceremony, so that we may suppose that they likewise do so
in the wooing; and in this case we can understand how it is that
they have been rendered the more beautiful. Mr. Meldola, from whom the
foregoing statements have been taken, says in conclusion: "Though I am
not convinced of the action of sexual selection in producing the
colours of insects, it cannot be denied that these facts are
strikingly corroborative of Mr. Darwin's views."*

  * Nature, April 27, 1871, p. 508. Mr. Meldola quotes Donzel, in Soc.
Ent. de France, 1837, p. 77, on the flight of butterflies whilst
pairing. See also Mr. G. Fraser, in Nature, April 20, 1871, p. 489, on
the sexual differences of several British butterflies.

  As sexual selection primarily depends on variability, a few words
must be added on this subject. In respect to colour there is no
difficulty, for any number of highly variable Lepidoptera could be
named. One good instance will suffice. Mr. Bates shewed me a whole
series of specimens of Papilio sesostris and P. childrenae; in the
latter the males varied much in the extent of the beautifully
enamelled green patch on the fore-wings, and in the size of the
white mark, and of the splendid crimson stripe on the hind-wings; so
that there was a great contrast amongst the males between the most and
the least gaudy. The male of Papilio sesostris is much less
beautiful than of P. childrenae; and it likewise varies a little in
the size of the green patch on the fore-wings, and in the occasional
appearance of the small crimson stripe on the hind-wings, borrowed, as
it would seem, from its own female; for the females of this and of
many other species in the Aeneas group possess this crimson stripe.
Hence between the brightest specimens of P. sesostris and the
dullest of P. childrenae, there was but a small interval; and it was
evident that as far as mere variability is concerned, there would be
no difficulty in permanently increasing the beauty of either species
by means of selection. The variability is here almost confined to
the male sex; but Mr. Wallace and Mr. Bates have shewn* that the
females of some species are extremely variable, the males being nearly
constant. In a future chapter I shall have occasion to shew that the
beautiful eye-like spots, or ocelli, found on the wings of many
Lepidoptera, are eminently variable. I may here add that these
ocelli offer a difficulty on the theory of sexual selection; for
though appearing to us so ornamental, they are never present in one
sex and absent in the other, nor do they ever differ much in the two
sexes.*(2) This fact is at present inexplicable; but if it should
hereafter be found that the formation of an ocellus is due to some
change in the tissues of the wings, for instance, occurring at a
very early period of development, we might expect, from what we know
of the laws of inheritance, that it would be transmitted to both
sexes, though arising and perfected in one sex alone.

[Bullseye]

* Wallace on the "Papilionidae of the Malayan Region," in
Transact. Linn. Soc., vol. xxv., 1865, pp. 8, 36. A striking case of a
rare variety, strictly intermediate between two other well-marked
female varieties, is given by Mr. Wallace. See also Mr. Bates, in
Proc. Entomolog. Soc., Nov. 19, 1866, p. xl.
  *(2) Mr. Bates was so kind as to lay this subject before the
Entomological Society, and I have received answers to this effect from
several entomologists.

  On the whole, although many serious objections may be urged, it
seems probable that most of the brilliantly-coloured species of
Lepidoptera owe their colours to sexual selection, excepting in
certain cases, presently to be mentioned, in which conspicuous colours
have been gained through mimicry as a protection. From the ardour of
the male throughout the animal kingdom, he is generally willing to
accept any female; and it is the female which usually exerts a choice.
Hence, if sexual selection has been efficient with the Lepidoptera,
the male, when the sexes differ, ought to be the more brilliantly
coloured, and this undoubtedly is the case. When both sexes are
brilliantly coloured and resemble each other, the characters
acquired by the males appear to have been transmitted to both. We
are led to this conclusion by cases, even within the same genus, of
gradation from an extraordinary amount of difference to identity in
colour between the two sexes.
  But it may be asked whether the difference in colour between the
sexes may not be accounted for by other means besides sexual
selection. Thus the males and females of the same species of butterfly
are in several cases known* to inhabit different stations, the
former commonly basking in the sunshine, the latter haunting gloomy
forests. It is therefore possible that different conditions of life
may have acted directly on the two sexes; but this is not probable*(2)
as in the adult state they are exposed to different conditions
during a very short period; and the larvae of both are exposed to
the same conditions. Mr. Wallace believes that the difference
between the sexes is due not so much to the males having been
modified, as to the females having in all or almost all cases acquired
dull colours for the sake of protection. It seems to me, on the
contrary, far more probable that it is the males which have been
chiefly modified through sexual selection, the females having been
comparatively little changed. We can thus understand how it is that
the females of allied species generally resemble one another so much
more closely than do the males. They thus shew us approximately the
primordial colouring of the parent-species of the group to which
they belong. They have, however, almost always been somewhat
modified by the transfer to them of some of the successive variations,
through the accumulation of which the males were rendered beautiful.
But I do not wish to deny that the females alone of some species may
have been specially modified for protection. In most cases the males
and females of distinct species will have been exposed during their
prolonged larval state to different conditions, and may have been thus
affected; though with the males any slight change of colour thus
caused will generally have been masked by the brilliant tints gained
through sexual selection. When we treat of birds, I shall have to
discuss the whole question, as to how far the differences in colour
between the sexes are due to the males having been modified through
sexual selection for ornamental purposes, or to the females having
been modified through natural selection for the sake of protection, so
that I will here say but little on the subject.

  * H. W. Bates, The Naturalist on the Amazons, vol. ii., 1863, p.
228. A. R. Wallace, in Transactions, Linnean Society, vol. xxv., 1865,
p. 10.
  *(2) On this whole subject see The Variation of Animals and Plants
under Domestication, 1868, vol. ii., chap. xxiii.

  In all the cases in which the more common form of equal
inheritance by both sexes has prevailed, the selection of
bright-coloured males would tend to make the females
bright-coloured; and the selection of dull-coloured females would tend
to make the males dull. If both processes were carried on
simultaneously, they would tend to counteract each other; and the
final result would depend on whether a greater number of females
from being well protected by obscure colours, or a greater number of
males by being brightly-coloured and thus finding partners,
succeeded in leaving more numerous offspring.
  In order to account for the frequent transmission of characters to
one sex alone, Mr. Wallace expresses his belief that the more common
form of equal inheritance by both sexes can be changed through natural
selection into inheritance by one sex alone, but in favour of this
view I can discover no evidence. We know from what occurs under
domestication that new characters often appear, which from the first
are transmitted to one sex alone; and by the selection of such
variations there would not be the slightest difficulty in giving
bright colours to the males alone, and at the same time or
subsequently, dull colours to the females alone. In this manner the
females of some butterflies and moths have, it is probable, been
rendered inconspicuous for the sake of protection, and widely
different from their males.
  I am, however, unwilling without distinct evidence to admit that two
complex processes of selection, each requiring the transference of new
characters to one sex alone, have been carried on with a multitude
of species,- that the males have been rendered more brilliant by
beating their rivals, and the females more dull-coloured by having
escaped from their enemies. The male, for instance, of the common
brimstone butterfly (Gonepteryx), is of a far more intense yellow than
the female, though she is equally conspicuous; and it does not seem
probable that she specially acquired her pale tints as a protection,
though it is probable that the male acquired his bright colours as a
sexual attraction. The female of Anthocharis cardamines does not
possess the beautiful orange wing-tips of the male; consequently she
closely resembles the white butterflies (Pieris) so common in our
gardens; but we have no evidence that this resemblance is beneficial
to her. As, on the other hand, she resembles both sexes of several
other species of the genus inhabiting various quarters of the world,
it is probable that she has simply retained to a large extent her
primordial colours.
  Finally, as we have seen, various considerations lead to the
conclusion that with the greater number of brilliantly-coloured
Lepidoptera it is the male which has been chiefly modified through
sexual selection; the amount of difference between the sexes mostly
depending on the form of inheritance which has prevailed.
Inheritance is govemed by so many unknown laws or conditions, that
it seems to us to act in a capricious manner;* and we can thus, to a
certain extent, understand how it is that with closely allied
species the sexes either differ to an astonishing degree, or are
identical in colour. As all the successive steps in the process of
variation are necessarily transmitted through the female, a greater or
less number of such steps might readily become developed in her; and
thus we can understand the frequent gradations from an extreme
difference to none at all between the sexes of allied species. These
cases of gradation, it may be added, are much too common to favour the
supposition that we here see females actually undergoing the process
of transition and losing their brightness for the sake of
protection; for we have every reason to conclude that at any one
time the greater number of species are in a fixed condition.

  * The Variation of Animals and Plants under Domestication, vol. ii.,
chap. xii., p. 17.

[Bullseye]

Mimicry.- This principle was first made clear in an admirable
paper by Mr. Bates,* who thus threw a flood of light on many obscure
problems. It had previously been observed that certain butterflies
in S. America belonging to quite distinct families, resembled the
Heliconidae so closely in every stripe and shade of colour, that
they could not be distinguished save by an experienced entomologist.
As the Heliconidae are coloured in their usual manner, whilst the
others depart from the usual colouring of the groups to which they
belong, it is clear that the latter are the imitators, and the
Heliconidae the imitated. Mr. Bates further observed that the
imitating species are comparatively rare, whilst the imitated
abound, and that the two sets live mingled together. From the fact
of the Heliconidae being conspicuous and beautiful insects, yet so
numerous in individuals and species, he concluded that they must be
protected from the attacks of enemies by some secretion or odour;
and this conclusion has now been amply confirmed,*(2) especially by
Mr. Belt. Hence Mr. Bates inferred that the butterflies which
imitate the protected species have acquired their present marvellously
deceptive appearance through variation and natural selection, in order
to be mistaken for the protected kinds, and thus to escape being
devoured. No explanation is here attempted of the brilliant colours of
the imitated, but only of the imitating butterflies. We must account
for the colours of the former in the same general manner, as in the
cases previously discussed in this chapter. Since the publication of
Mr. Bates's paper, similar and equally striking facts have been
observed by Mr. Wallace in the Malayan region, by Mr. Trimen in
South Africa, and by Mr. Riley in the United States.*(3)

  * Transact. Linn. Soc., vol. xxiii., 1862, p. 495.
  *(2) Proc. Entomological Soc., Dec. 3, 1866, p. xlv.
  *(3) Wallace, Transact. Linn. Soc., vol. xxv., 1865 p. i.; also,
Transact. Ent. Soc., vol. iv., 3rd series: 1867, p. 301. Trimen, Linn.
Transact., vol. xxvi., 1869, p. 497. Riley, Third Annual Report on the
Noxious Insects of Missouri, 1871, pp. 163-168. This latter essay is
valuable, as Mr. Riley here discusses all the objections which have
been raised against Mr. Bates's theory.

  As some writers have felt much difficulty in understanding how the
first steps in the process of mimicry could have been effected through
natural selection, it may be well to remark that the process
probably commenced long ago between forms not widely dissimilar in
colour. In this case even a slight variation would be beneficial, if
it rendered the one species more like the other; and afterwards the
imitated species might be modified to an extreme degree through sexual
selection or other means, and if the changes were gradual, the
imitators might easily be led along the same track, until they
differed to an equally extreme degree from their original condition;
and they would thus ultimately assume an appearance or colouring
wholly unlike that of the other members of the group to which they
belonged. It should also be remembered that many species of
Lepidoptera are liable to considerable and abrupt variations in
colour. A few instances have been given in this chapter; and many more
may be found in the papers of Mr. Bates and Mr. Wallace.
  With several species the sexes are alike, and imitate the two
sexes of another species. But Mr. Trimen gives, in the paper already
referred to, three cases in which the sexes of the imitated form
differ from each other in colour, and the sexes of the imitating
form differ in a like manner. Several cases have also been recorded
where the females alone imitate brilliantly-coloured and protected
species, the males retaining "the normal aspect of their immediate
congeners." It is here obvious that the successive variations by which
the female has been modified have been transmitted to her alone. It
is, however, probable that some of the many successive variations
would have been transmitted to, and developed in, the males had not
such males been eliminated by being thus rendered less attractive to
the females; so that only those variations were preserved which were
from the first strictly limited in their transmission to the female
sex. We have a partial illustration of these remarks in a statement by
Mr. Belt;* that the males of some of the Leptalides, which imitate
protected species, still retain in a concealed manner some of their
original characters. Thus in the males "the upper half of the lower
wing is of a pure white, whilst all the rest of the wings is barred
and spotted with black, red and yellow, like the species they mimic.
The females have not this white patch, and the males usually conceal
it by covering it with the upper wing, so that I cannot imagine its
being of any other use to them than as an attraction in courtship,
when they exhibit it to the females, and thus gratify their
deep-seated preference for the normal colour of the Order to which the
Leptalides belong."

  * The Naturalist in Nicaragua, 1874, p. 385.

  Bright Colours of Caterpillars.- Whilst reflecting on the beauty
of many butterflies, it occurred to me that some caterpillars were
splendidly coloured; and as sexual selection could not possibly have
here acted, it appeared rash to attribute the beauty of the mature
insect to this agency, unless the bright colours of their larvae could
be somehow explained. In the first place, it may be observed that
the colours of caterpillars do not stand in any close correlation with
those of the mature insect. Secondly, their bright colours do not
serve in any ordinary manner as a protection. Mr. Bates informs me, as
an instance of this, that the most conspicuous caterpillar which he
ever beheld (that of a sphinx) lived on the large green leaves of a
tree on the open llanos of South America; it was about four inches
in length, transversely banded with black and yellow, and with its
head, legs, and tail of a bright red. Hence it caught the eye of any
one who passed by, even at the distance of many yards, and no doubt
that of every passing bird.
  I then applied to Mr. Wallace, who has an innate genius for
solving difficulties. After some consideration he replied: "Most
caterpillars require protection, as may be inferred from some kinds
being furnished with spines or irritating hairs, and from many being
coloured green like the leaves on which they feed, or being
curiously like the twigs of the trees on which they live." Another
instance of protection, furnished me by Mr. J. Mansel Weale, may be
added, namely, that there is a caterpillar of a moth which lives on
the mimosas in South Africa, and fabricates for itself a case quite
indistinguishable from the surrounding thorns. From such
considerations Mr. Wallace thought it probable that conspicuously
coloured caterpillars were protected by having a nauseous taste; but
as their skin is extremely tender, and as their intestines readily
protrude from a wound, a slight peck from the beak of a bird would
be as fatal to them as if they had been devoured. Hence, as Mr.
Wallace remarks, "distastefulness alone would be insufficient to
protect a caterpillar unless some outward sign indicated to its
would-be destroyer that its prey was a disgusting morsel." Under these
circumstances it would be highly advantageous to a caterpillar to be
instantaneously and certainly recognised as unpalatable by all birds
and other animals. Thus the most gaudy colours would be serviceable,
and might have been gained by variation and the survival of the most
easily-recognised individuals.
  This hypothesis appears at first sight very bold, but when it was
brought before the Entomological Society* it was supported by
various statements; and Mr. J. Jenner Weir, who keeps a large number
of birds in an aviary, informs me that he has made many trials, and
finds no exception to the rule, that all caterpillars of nocturnal and
retiring habits with smooth skins, all of a green colour, and all
which imitate twigs, are greedily devoured by his birds. The hairy and
spinose kinds are invariably rejected, as were four
conspicuously-coloured species. When the birds rejected a caterpillar,
they plainly shewed, by shaking their heads, and cleansing their
beaks, that they were disgusted by the taste.*(2) Three conspicuous
kinds of caterpillars and moths were also given to some lizards and
frogs, by Mr. A. Butler, and were rejected, though other kinds were
eagerly eaten. Thus the probability of Mr. Wallace's view is
confirmed, namely, that certain caterpillars have been made
conspicuous for their own good, so as to be easily recognised by their
enemies, on nearly the same principle that poisons are sold in
coloured bottles by druggists for the good of man. We cannot, however,
at present thus explain the elegant diversity in the colours of many
caterpillars; but any species which had at some former period acquired
a dull, mottled, or striped appearance, either in imitation of
surrounding objects, or from the direct action of climate, &c., almost
certainly would not become uniform in colour when its tints were
rendered intense and bright; for in order to make a caterpillar merely
conspicuous, there would be no selection in any definite direction.

  * Proceedings, Entomological Society, Dec. 3, 1866, p. xlv., and
March 4, 1867, p. lxxx.
  *(2) See Mr. J. Jenner Weir's Paper on "Insects and Insectivorus
Birds," in Transact. Ent. Soc., 1869, p. 21; also Mr. Butler's
paper, ibid., p. 27. Mr. Riley has given analogous facts in the
Third Annual Report on the Noxious Insects of Missouri, 1871, p.
148. Some opposed cases are, however, given by Dr. Wallace and M. H.
d'Orville; see Zoological Record, 1869, p. 349.

  Summary and Concluding Remarks on Insects.- Looking back to the
several Orders, we see that the sexes often differ in various
characters, the meaning of which is not in the least understood. The
sexes, also, often differ in their organs of sense and means of
locomotion, so that the males may quickly discover and reach the
females. They differ still oftener in the males possessing diversified
contrivances for retaining the females when found. We are, however,
here concerned only in a secondary degree with sexual differences of
these kinds.
  In almost all the Orders, the males of some species, even of weak
and delicate kinds, are known to be highly pugnacious; and some few
are furnished with special weapons for fighting with their rivals. But
the law of battle does not prevail nearly so widely with insects as
with the higher animals. Hence it probably arises, that it is in
only a few cases that the males have been rendered larger and stronger
than the females. On the contrary, they are usually smaller, so that
they may be developed within a shorter time, to be ready in large
numbers for the emergence of the females.
  In two families of the Homoptera and in three of the Orthoptera, the
males alone possess sound-producing organs in an efficient state.
These are used incessantly during the breeding-season, not only for
calling the females, but apparently for charming or exciting them in
rivalry with other males. No one who admits the agency of selection of
any kind, will, after reading the above discussion, dispute that these
musical instruments have been acquired through sexual selection. In
four other Orders the members of one sex, or more commonly of both
sexes, are provided with organs for producing various sounds, which
apparently serve merely as call-notes. When both sexes are thus
provided, the individuals which were able to make the loudest or
most continuous noise would gain partners before those which were less
noisy, so that their organs have probably been gained through sexual
selection. It is instructive to reflect on the wonderful diversity
of the means for producing sound, possessed by the males alone, or
by both sexes, in no less than six Orders. We thus learn how effectual
sexual selection has been in leading to modifications which sometimes,
as with the Homoptera, relate to important parts of the organisation.
  From the reasons assigned in the last chapter, it is probable that
the great horns possessed by the males of many lamellicorn, and some
other beetles, have been acquired as ornaments. From the small size of
insects, we are apt to undervalue their appearance. If we could
imagine a male Chalcosoma (see fig. 16), with its polished bronzed
coat of mail, and its vast complex horns, magnified to the size of a
horse, or even of a dog, it would be one of the most imposing
animals in the world.

[Bullseye]

The colouring of insects is a complex and obscure subject. When
the male differs slightly from the female, and neither are
brilliantly-coloured, it is probable that the sexes have varied in a
slightly different manner, and that the variations have been
transmitted by each sex to the same without any benefit or evil thus
accruing. When the male is brilliantly-coloured and differs
conspicuously from the female, as with some dragonflies and many
butterflies, it is probable that he owes his colours to sexual
selection; whilst the female has retained a primordial or very ancient
type of colouring, slightly modified by the agencies before explained.
But in some cases the female has apparently been made obscure by
variations transmitted to her alone, as a means of direct
protection; and it is almost certain that she has sometimes been
made brilliant, so as to imitate other protected species inhabiting
the same district. When the sexes resemble each other and both are
obscurely coloured, there is no doubt that they have been in a
multitude of cases so coloured for the sake of protection. So it is in
some instances when both are brightly-coloured, for they thus
imitate protected species, or resemble surrounding objects such as
flowers; or they give notice to their enemies that they are
unpalatable. In other cases in which the sexes resemble each other and
are both brilliant, especially when the colours are arranged for
display, we may conclude that they have been gained by the male sex as
an attraction, and have been transferred to the female. We are more
especially led to this conclusion whenever the same type of coloration
prevails throughout a whole group, and we find that the males of
some species differ widely in colour from the females, whilst others
differ slightly or not at all with intermediate gradations
connecting these extreme states.
  In the same manner as bright colours have often been partially
transferred from the males to the females, so it has been with the
extraordinary horns of many lamellicorn and some other beetles. So
again, the sound-producing organs proper to the males of the Homoptera
and Orthoptera have generally been transferred in a rudimentary, or
even in a nearly perfect condition, to the females; yet not
sufficiently perfect to be of any use. It is also an interesting fact,
as bearing on sexual selection, that the stridulating organs of
certain male Orthoptera are not fully developed until the last
moult; and that the colours of certain male dragon-flies are not fully
developed until some little time after their emergence from the
pupal state, and when they are ready to breed.
  Sexual selection implies that the more attractive individuals are
preferred by the opposite sex; and as with insects, when the sexes
differ, it is the male which, with some rare exceptions, is the more
ornamented, and departs more from the type to which the species
belongs;- and as it is the male which searches eagerly for the female,
we must suppose that the females habitually or occasionally prefer the
more beautiful males, and that these have thus acquired their
beauty. That the females in most or all the Orders would have the
power of rejecting any particular male, is probable from the many
singular contrivances possessed by the males, such as great jaws,
adhesive cushions, spines, elongated legs, &c., for seizing the
female; for these contrivances shew that there is some difficulty in
the act, so that her concurrence would seem necessary. Judging from
what we know of the perceptive powers and affections of various
insects, there is no antecedent improbability in sexual selection
having come largely into play; but we have as yet no direct evidence
on this head, and some facts are opposed to the belief.
Nevertheless, when we see many males pursuing the same female, we
can hardly believe that the pairing is left to blind chance- that
the female exerts no choice, and is not influenced by the gorgeous
colours or other ornaments with which the male is decorated.
  If we admit that the females of the Homoptera and Orthoptera
appreciate the musical tones of their male partners, and that the
various instruments have been perfected through sexual selection,
there is little improbability in the females of other insects
appreciating beauty in form or colour, and consequently in such
characters having been thus gained by the males. But from the
circumstance of colour being so variable, and from its having been
so often modified for the sake of protection, it is difficult to
decide in how large a proportion of cases sexual selection has
played a part. This is more especially difficult in those Orders, such
as Orthoptera, Hymenoptera, and Coleoptera, in which the two sexes
rarely differ much in colour; for we are then left to mere analogy.
With the Coleoptera, however, as before remarked, it is in the great
lamellicorn group, placed by some authors at the head of the Order,
and in which we sometimes see a mutual attachment between the sexes,
that we find the males of some species possessing weapons for sexual
strife, others furnished with wonderful horns, many with
stridulating organs, and others ornamented with splendid metallic
tints. Hence it seems probable that all these characters have been
gained through the same means, namely sexual selection. With
butterflies we have the best evidence, as the males sometimes take
pains to display their beautiful colours; and we cannot believe that
they would act thus, unless the display was of use to them in their
courtship.
  When we treat of birds, we shall see that they present in their
secondary sexual characters the closest analogy with insects. Thus,
many male birds are highly pugnacious, and some are furnished with
special weapons for fighting with their rivals. They possess organs
which are used during the breeding-season for producing vocal and
instrumental music. They are frequently ornamented with combs,
horns, wattles and plumes of the most diversified kinds, and are
decorated with beautiful colours, all evidently for the sake of
display. We shall find that, as with insects, both sexes in certain
groups are equally beautiful, and are equally provided with
ornaments which are usually confined to the male sex. In other
groups both sexes are equally plain-coloured and unornamented. Lastly,
in some few anomalous cases, the females are more beautiful than the
males. We shall often find, in the same group of birds, every
gradation from no difference between the sexes, to an extreme
difference. We shall see that female birds, like female insects, often
possess more or less plain traces or rudiments of characters which
properly belong to the males and are of use only to them. The analogy,
indeed, in all these respects between birds and insects is curiously
close. Whatever explanation applies to the one class probably
applies to the other; and this explanation, as we shall hereafter
attempt to shew in further detail, is sexual selection.



--------------------------------------------------------------------------------

[Bullseye]

Chapter XII Secondary Sexual Characteristics of Fishes, Amphibians, and Reptiles

  WE have now arrived at the great sub-kingdom of the Vertebrata,
and will commence with the lowest class, that of fishes. The males
of plagiostomous fishes (sharks, rays) and of chimaeroid fishes are
provided with claspers which serve to retain the female, like the
various structures possessed by many of the lower animals. Besides the
claspers, the males of many rays have clusters of strong sharp
spines on their heads, and several rows along "the upper outer surface
of their pectoral fins." These are present in the males of some
species, which have other parts of their bodies smooth. They are
only temporarily developed during the breeding-season; and Dr. Gunther
suspects that they are brought into action as prehensile organs by the
doubling inwards and downwards of the two sides of the body. It is a
remarkable fact that the females and not the males of some species, as
of Raia clavata, have their backs studded with large hook-formed
spines.*

  * Yarrell's Hist. of British Fishes, vol. ii., 1836, pp 417, 425,
436. Dr. Gunther informs me that the spines in R. clavata are peculiar
to the female.

  The males alone of the capelin (Mallotus villosus, one of
Salmonidae), are provided with a ridge of closely-set, brush-like
scales, by the aid of which two males, one on each side, hold the
female, whilst she runs with great swiftness on the sandy beach, and
there deposits her spawn.* The widely distinct Monacanthus scopas
presents a somewhat analogous structure. The male, as Dr. Gunther
informs me, has a cluster of stiff, straight spines, like those of a
comb, on the sides of the tail; and these in a specimen six inches
long were nearly one and a half inches in length; the female has in
the same place a cluster of bristles, which may be compared with those
of a tooth-brush. In another species, M. peronii, the male has a brush
like that possessed by the female of the last species, whilst the
sides of the tail in the female are smooth. In some other species of
the same genus the tail can be perceived to be a little roughened in
the male and perfectly smooth in the female; and lastly in others,
both sexes have smooth sides.

  * The American Naturalist, April, 1871, p. 119.

  The males of many fish fight for the possession of the females. Thus
the male stickleback (Gasterosteus leiurus) has been described as "mad
with delight," when the female comes out of her hiding-place and
surveys the nest which he has made for her. "He darts round her in
every direction, then to his accumulated materials for the nest,
then back again in an instant; and as she does not advance he
endeavours to push her with his snout, and then tries to pull her by
the tail and side-spine to the nest."* The males are said to be
polygamists;*(2) they are extraordinarily bold and pugnacious,
whilst "the females are quite pacific." Their battles are at times
desperate; "for these puny combatants fasten tight on each other for
several seconds, tumbling over and over again until their strength
appears completely exhausted." With the rough-tailed stickleback (G.
trachurus) the males whilst fighting swim round and round each
other, biting and endeavouring to pierce each other with their
raised lateral spines. The same writer adds,*(3) "the bite of these
little furies is very severe. They also use their lateral spines
with such fatal effect, that I have seen one during a battle
absolutely rip his opponent quite open, so that he sank to the
bottom and died." When a fish is conquered, "his gallant bearing
forsakes him; his gay colours fade away; and he hides his disgrace
among his peaceable companions, but is for some time the constant
object of his conqueror's persecution."

  * See Mr, R. Warington's interesting articles in Annals and Magazine
of Natural History, October, 1852, and November, 1855.
  *(2) Noel Humphreys. River Gardens, 1857.
  *(3) Loudon's Magazine of Natural History, vol. iii., 1830, p. 331.

  The male salmon is as pugnacious as the little stickleback; and so
is the male trout, as I hear from Dr. Gunther. Mr. Shaw saw a
violent contest between two male salmon which lasted the whole day;
and Mr. R. Buist, Superintendent of Fisheries, informs me that he
has often watched from the bridge at Perth the males driving away
their rivals, whilst the females were spawning The males "are
constantly fighting and tearing each other on the spawning-beds, and
many so injure each other as to cause the death of numbers, many being
seen swimming near the banks of the river in a state of exhaustion,
and apparently in a dying state."* Mr. Buist informs me, that in
June 1868, the keeper of the Stormontfield breeding-ponds visited
the northern Tyne and found about 300 dead salmon, all of which with
one exception were males; and he was convinced that they had lost
their lives by fighting.

  * The Field, June 29, 1867. For Mr. Shaw's statements, see Edinburgh
Review, 1843. Another experienced observer (Scrope's Days of Salmon
Fishing, p. 60) remarks that like the stag, the male would, if he
could, keep all other males away.

  The most curious point about the male salmon is that during the
breeding-season, besides a slight change in colour, "the lower jaw
elongates, and a cartilaginous projection turns upwards from the
point, which, when the jaws are closed, occupies a deep cavity between
the intermaxillary bones of the upper jaw."* (See figs. 27 and 28.) In
our salmon this change of structure lasts only during the
breeding-season; but in the Salmo lycaodon of N. W. America the
change, as Mr. J. K. Lord*(2) believes, is permanent, and best
marked in the older males which have previously ascended the rivers.
In these old males the jaw becomes developed into an immense hook-like
projection, and the teeth grow into regular fangs, often more than
half an inch in length. With the European salmon, according to Mr.
Lloyd,*(3) the temporary hook-like structure serves to strengthen
and protect the jaws, when one male charges another with wonderful
violence; but the greatly developed teeth of the male American
salmon may be compared with the tusks of many male mammals, and they
indicate an offensive rather than a protective purpose.

  * Yarrell, History of British Fishes, vol. ii., 1836, p. 10.
  *(2) The Naturalist in Vancouver's Island, vol. i., 1866, p. 54.
  *(3) Scandinavian Adventures, vol. i., 1854, pp. 100, 104.

  The salmon is not the only fish in which the teeth differ in the two
sexes; as this is the case with many rays. In the thornback (Raia
clavata) the adult male has sharp, pointed teeth, directed
backwards, whilst those of the female are broad and flat, and form a
pavement; so that these teeth differ in the two sexes of the same
species more than is usual in distinct genera of the same family.
The teeth of the male become sharp only when he is adult: whilst young
they are broad and flat like those of the female. As so frequently
occurs with secondary sexual characters, both sexes of some species of
rays (for instance R. batis), when adult, possess sharp pointed teeth;
and here a character, proper to and primarily gained by the male,
appears to have been transmitted to the offspring of both sexes. The
teeth are likewise pointed in both sexes of R. maculata, but only when
quite adult; the males acquiring them at an earlier age than the
females. We shall hereafter meet with analogous cases in certain
birds, in which the male acquires the plumage common to both sexes
when adult, at a somewhat earlier age than does the female. With other
species of rays the males even when old never possess sharp teeth, and
consequently the adults of both sexes are provided with broad, flat
teeth like those of the young, and like those of the mature females of
the above-mentioned species.* As the rays are bold, strong and
voracious fish, we may suspect that the males require their sharp
teeth for fighting with their rivals; but as they possess many parts
modified and adapted for the prehension of the female, it is
possible that their teeth may be used for this purpose.

  * See Yarrell's account of the rays in his History of British
Fishes, vol. ii., 1836, p. 416, with an excellent figure, and pp. 422,
432.

  In regard to size, M. Carbonnier* maintains that the female of
almost all fishes is larger than the male; and Dr. Gunther does not
know of a single instance in which the male is actually larger than
the female. With some cyprinodonts the male is not even half as large.
As in many kinds of fishes the males habitually fight together, it
is surprising that they have not generally become larger and
stronger than the females through the effects of sexual selection. The
males suffer from their small size, for according to M. Carbonnier,
they are liable to be devoured by the females of their own species
when carnivorous, and no doubt by other species. Increased size must
be in some manner of more importance to the females, than strength and
size are to the males for fighting with other males; and this
perhaps is to allow of the production of a vast number of ova.

  * As quoted in the Farmer, 1868, p. 369.

  In many species the male alone is ornamented with bright colours; or
these are much brighter in the male than the female. The male, also,
is sometimes provided with appendages which appear to be of no more
use to him for the ordinary purposes of life, than are the tail
feathers to the peacock. I am indebted for most of the following facts
to the kindness of Dr. Gunther. There is reason to suspect that many
tropical fishes differ sexually in colour and structure; and there are
some striking cases with our British fishes. The male Callionymus lyra
has been called the gemmeous dragonet "from its brilliant gem-like
colours." When fresh caught from the sea the body is yellow of various
shades, striped and spotted with vivid blue on the head; the dorsal
fins are pale brown with dark longitudinal bands; the ventral, caudal,
and anal fins being bluish-black. The female, or sordid dragonet,
was considered by Linnaeus, and by many subsequent naturalists, as a
distinct species; it is of a dingy reddish-brown, with the dorsal
fin brown and the other fins white. The sexes differ also in the
proportional size of the head and mouth, and in the position of the
eyes;* but the most striking difference is the extraordinary
elongation in the male (see fig. 29) of the dorsal fin. Mr. W. Saville
Kent remarks that this "singular appendage appears from my
observations of the species in confinement, to be subservient to the
same end as the wattles, crests, and other abnormal adjuncts of the
male in gallinaceous birds, for the purpose of fascinating their
mates."*(2) The young males resemble the adult females in structure
and colour. Throughout the genus Callionymus,*(3) the male is
generally much more brightly spotted than the female, and in several
species, not only the dorsal, but the anal fin is much elongated in
the males.

  * I have drawn up this description from Yarrell's British Fishes,
vol. i., 1836, pp. 261 and 266.
  *(2) Nature, July, 1873, p. 264.
  *(3) Catalogue of Acanth. Fishes in the British Museum, by Dr.
Gunther, 1861, pp. 138-151.

  The male of the Cottus scorpius, or sea-serpent, is slenderer and
smaller than the female. There is also a great difference in colour
between them. It is difficult, as Mr. Lloyd* remarks, "for any one,
who has not seen this fish during the spawning-season, when its hues
are brightest, to conceive the admixture of brilliant colours with
which it, in other respects so ill-favoured, is at that time
adorned. Both sexes of the Labrus mixtus, although very different in
colour, are beautiful; the male being orange with bright blue stripes,
and the female bright red with some black spots on the back.

  * Game Birds of Sweden, &c., 1867, p. 466.

[Bullseye]

In the very distinct family of the Cyprinodontidae- inhabitants of
the fresh waters of foreign lands- the sexes sometimes differ much
in various characters. In the male of the Mollienesia petenensis,* the
dorsal fin is greatly developed and is marked with a row of large,
round, ocellated, bright-coloured spots; whilst the same fin in the
female is smaller, of a different shape, and marked only with
irregularly curved brown spots. In the male the basal margin of the
anal fin is also a little produced and dark coloured. In the male of
an allied form, the Xiphophorus Hellerii (see fig. 30), the inferior
margin of the caudal fin is developed into a long filament, which,
as I hear from Dr. Gunther, is striped with bright colours. This
filament does not contain any muscles, and apparently cannot be of any
direct use to the fish. As in the case of the Callionymus, the males
whilst young resemble the adult females in colour and structure.
Sexual differences such as these may be strictly compared with those
which are so frequent with gallinaceous birds.*(2)

  * With respect to this and the following species I am indebted to
Dr. Gunther for information: see also his paper on the "Fishes of
Central America," in Transact. Zoological Soc., vol. vi., 1868, p.
485.
  *(2) Dr. Gunther makes this remark, Catalogue of Fishes in the
British Museum, vol. iii., 1861, p. 141.

  In a siluroid fish, inhabiting the fresh waters of South America,
the Plecostomus barbatus* (see fig. 31), the male has its mouth and
interoperculum fringed with a beard of stiff hairs, of which the
female shows hardly a trace. These hairs are of the nature of
scales. In another species of the same genus, soft flexible
tentacles project from the front part of the head of the male, which
are absent in the female. These tentacles are prolongations of the
true skin, and therefore are not homologous with the stiff hairs of
the former species; but it can hardly be doubted that both serve the
same purpose. What this purpose may be, is difficult to conjecture;
ornament does not here seem probable, but we can hardly suppose that
stiff hairs and flexible filaments can be useful in any ordinary way
to the males alone. In that strange monster, the Chimaera monstrosa,
the male has a hook-shaped bone on the top of the head, directed
forwards, with its end rounded and covered with sharp spines; in the
female "this crown is altogether absent," but what its use may be to
the male is utterly unknown.*(2)

  * See Dr. Gunther on this genus, in Proceedings of the Zoological
Society, 1868, p. 232.
  *(2) F. Buckland, in Land and Water, July, 1868, p. 377, with a
figure. Many other cases could be added of structures peculiar to
the male, of which the uses are not known.

  The structures as yet referred to are permanent in the male after he
has arrived at maturity; but with some blennies, and in another allied
genus,* a crest is developed on the head of the male only during the
breeding-season, and the body at the same time becomes more
brightly-coloured. There can be little doubt that this crest serves as
a temporary sexual ornament, for the female does not exhibit a trace
of it. In other species of the same genus both sexes possess a
crest, and in at least one species neither sex is thus provided. In
many of the Chromidae, for instance in Geophagus and especially in
Cichla, the males, as I hear from Professor Agassiz,*(2) have a
conspicuous protuberance on the forehead, which is wholly wanting in
the females and in the young males. Professor Agassiz adds, "I have
often observed these fishes at the time of spawning when the
protuberance is largest, and at other seasons when it is totally
wanting, and the two sexes shew no difference whatever in the
outline of the profile of the head. I never could ascertain that it
subserves any special function, and the Indians on the Amazon know
nothing about its use." These protuberances resemble, in their
periodical appearance, the fleshy carbuncles on the heads of certain
birds; but whether they serve as ornaments must remain at present
doubtful.

   * Dr. Gunther, Catalogue of Fishes, vol. iii., pp. 221 and 240.
  *(2) See also A Journey in Brazil, by Prof. and Mrs. Agassiz,
1868, p. 220.

  I hear from Professor Agassiz and Dr. Gunther, that the males of
those fishes, which differ permanently in colour from the females,
often become more brilliant during the breeding-season. This is
likewise the case with a multitude of fishes, the sexes of which are
identical in colour at all other seasons of the year. The tench,
roach, and perch may be given as instances. The male salmon at this
season is marked on the cheeks with orange-coloured stripes, which
give it the appearance of a Labrus, and the body partakes of a
golden orange tinge. The females are dark in colour, and are
commonly called black-fish."* An analogous and even greater change
takes place with the Salmo eriox or bull trout; the males of the
char (S. umbla) are likewise at this season rather brighter in
colour than the females.*(2) The colours of the pike (Esox
reticulatus) of the United States, especially of the male, become,
during the breeding-season, exceedingly intense, brilliant, and
iridescent.*(3) Another striking instance out of many is afforded by
the male stickleback (Gasterosteus leiurus), which is described by Mr.
Warington,*(4) as being then "beautiful beyond description." The
back and eyes of the female are simply brown and the belly white.
The eyes of the male, on the other hand, are "of the most splendid
green, having a metallic lustre like the green feathers of some
humming-birds. The throat and belly are of a bright crimson, the
back of an ashy-green, and the whole fish appears as though it were
somewhat translucent and glowed with an internal incandescence." After
the breeding-season these colours all change, the throat and belly
become of a paler red, the back more green, and the glowing tints
subside.

[Bullseye]

* Yarrell, History of British Fishes, vol. ii., 1836, pp. 10, 12,
35.
  *(2) W. Thompson, in Annals and Magazine of Natural History, vol.
vi., 1841, p. 440.
  *(3) The American Agriculturalist, 1868, p. 100.
  *(4) Annals and Mag. of Nat. Hist., Oct., 1852.

  With respect to the courtship of fishes, other cases have been
observed since the first edition of this book appeared, besides that
already given of the stickleback. Mr. W. S. Kent says that the male of
the Labrus mixtus, which, as we have seen, differs in colour from
the female, makes "a deep hollow in the sand of the tank, and then
endeavours in the most persuasive manner to induce a female of the
same species to share it with him, swimming backwards and forwards
between her and the completed nest, and plainly exhibiting the
greatest anxiety for her to follow." The males of Cantharus lineatus
become, during the breeding-season, of deep leaden-black; they then
retire from the shoal, and excavate a hollow as a nest. "Each male now
mounts vigilant guard over his respective hollow, and vigorously
attacks and drives away any other fish of the same sex. Towards his
companions of the opposite sex his conduct is far different; many of
the latter are now distended with spawn, and these he endeavours by
all the means in his power to lure singly to his prepared hollow,
and there to deposit the myriad ova with which they are laden, which
he then protects and guards with the greatest care."*

  * Nature, May, 1873, p. 25.

  A more striking case of courtship, as well as of display, by the
males of a Chinese Macropus has been given by M. Carbonnier, who
carefully observed these fishes under confinement.* The males are most
beautifully coloured, more so than the females. During the
breeding-season they contend for the possession of the females; and,
in the act of courtship, expand their fins, which are spotted and
ornamented with brightly coloured rays, in the same manner,
according to M. Carbonnier, as the peacock. They then also bound about
the females with much vivacity, and appear by "l'etalage de leurs
vives couleurs chercher a attirer l'attention des femelles, lesquelles
ne paraissaient indifferentes a ce manege, elles nageaient avec une
molle lenteur vers les males et semblaient se complaire dans leur
voisinage." After the male has won his bride, he makes a little disc
of froth by blowing air and mucus out of his mouth. He then collects
the fertilised ova, dropped by the female, in his mouth; and this
caused M. Carbonnier much alarm, as he thought that they were going to
be devoured. But the male soon deposits them in the disc of froth,
afterwards guarding them, repairing the froth, and taking care of
the young when hatched. I mention these particulars because, as we
shall presently see, there are fishes, the males of which hatch
their eggs in their mouths; and those who do not believe in the
principle of gradual evolution might ask how could such a habit have
originated; but the difficulty is much diminished when we know that
there are fishes which thus collect and carry the eggs; for if delayed
by any cause in depositing them, the habit of hatching them in their
mouths might have been acquired.

  * Bulletin de la Societe d'Acclimation, Paris, July, 1869, and Jan.,
1870.

  To return to our more immediate subject. The case stands thus:
female fishes, as far as I can learn, never willingly spawn except
in the presence of the males; and the males never fertilise the ova
except in the presence of the females. The males fight for the
possession of the females. In many species, the males whilst young
resemble the females in colour; but when adult become much more
brilliant, and retain their colours throughout life. In other
species the males become brighter than the females and otherwise
more highly ornamented, only during the season of love. The males
sedulously court the females, and in one case, as we have seen, take
pains in displaying their beauty before them. Can it be believed
that they would thus act to no purpose during their courtship? And
this would be the case, unless the females exert some choice and
select those males which please or excite them most. If the female
exerts such choice, all the above facts on the ornamentation of the
males become at once intelligible by the aid of sexual selection.
  We have next to inquire whether this view of the bright colours of
certain male fishes having been acquired through sexual selection can,
through the law of the equal transmission of characters to both sexes,
be extended to those groups in which the males and females are
brilliant in the same, or nearly the same degree and manner. In such a
genus as Labrus, which includes some of the most splendid fishes in
the world- for instance, the peacock Labrus (L. pavo), described,*
with pardonable exaggeration, as formed of polished scales of gold,
encrusting lapis-lazuli, rubies, sapphires, emeralds, and amethysts-
we may, with much probability, accept this belief; for we have seen
that the sexes in at least one species of the genus differ greatly
in colour. With some fishes, as with many of the lowest animals,
splendid colours may be the direct result of the nature of their
tissues and of the surrounding conditions, without the aid of
selection of any kind. The gold-fish (Cyprinus auratus), judging
from the analogy of the golden variety of the common carp, is
perhaps a case in point, as it may owe its splendid colours to a
single abrupt variation, due to the conditions to which this fish
has been subjected under confinement. It is, however, more probable
that these colours have been intensified through artificial selection,
as this species has been carefully bred in China from a remote
period.*(2) Under natural conditions it does not seem probable that
beings so highly organised as fishes, and which live under such
complex relations, should become brilliantly coloured without
suffering some evil or receiving some benefit from so great a
change, and consequently without the intervention of natural
selection.

  * Bory de Saint Vincent, in Dict. Class. d'Hist. Nat., tom. ix.,
1826, p. 151.
  *(2) Owing to some remarks on this subject, made in my work On the
Variation of Animals under Domestication, Mr. W. F. Mayers (Chinese
Notes and Queries, Aug., 1868, p. 123) has searched the ancient
Chinese encyclopedias. He finds that gold-fish were first reared in
confinement during the Sung Dynasty, which commenced A.D. 960. In
the year 1129 these fishes abounded. In another place it is said
that since the year 1548 there has been "produced at Hangchow a
variety called the fire-fish, from its intensely red colour. It is
universally admired, and there is not a household where it is not
cultivated, in rivalry as to its colour, and as a source of profit."

  What, then, are we to conclude in regard to the many fishes, both
sexes of which are splendidly coloured? Mr. Wallace* believes that the
species which frequent reefs, where corals and other brightly-coloured
organisms abound, are brightly coloured in order to escape detection
by their enemies; but according to my recollection they were thus
rendered highly conspicuous. In the fresh-waters of the tropics
there are no brilliantly-coloured corals or other organisms for the
fishes to resemble; yet many species in the Amazons are beautifully
coloured, and many of the carnivorous Cyprinidae in India are
ornamented with "bright longitudinal lines of various tints."*(2)
Mr. M'Clelland, in describing these fishes, goes so far as to
suppose that "the peculiar brilliancy of their colours" serves as "a
better mark for king-fishers, terns, and other birds which are
destined to keep the number of these fishes in check"; but at the
present day few naturalists will admit that any animal has been made
conspicuous as an aid to its own destruction. It is possible that
certain fishes may have been rendered conspicuous in order to warn
birds and beasts of prey that they were unpalatable, as explained when
treating of caterpillars; but it is not, I believe, known that any
fish, at least any fresh-water fish, is rejected from being
distasteful to fish-devouring animals. On the whole, the most probable
view in regard to the fishes, of which both sexes are brilliantly
coloured, is that their colours were acquired by the males as a sexual
ornament, and were transferred equally, or nearly so, to the other
sex.

[Bullseye]

* Westminster Review, July, 1867, p. 7.
  *(2) "Indian Cyprinidae," by Mr. M'Clelland, Asiatic Researches,
vol. xix., part ii., 1839, p. 230.

  We have now to consider whether, when the male differs in a marked
manner from the female in colour or in other ornaments, he alone has
been modified, the variations being inherited by his male offspring
alone; or whether the female has been specially modified and
rendered inconspicuous for the sake of protection, such
modifications being inherited only by the females. It is impossible to
doubt that colour has been gained by many fishes as a protection: no
one can examine the speckled upper surface of a flounder, and overlook
its resemblance to the sandy bed of the sea on which it lives. Certain
fishes, moreover, can through the action of the nervous system
change their colours in adaptation to surrounding objects, and that
within a short time.* One of the most striking instances ever recorded
of an animal being protected by its colour (as far as it can be judged
of in preserved specimens), as well as by its form, is that given by
Dr. Gunther*(2) of a pipe-fish, which, with its reddish streaming
filaments, is hardly distinguishable from the sea-weed to which it
clings with its prehensile tail. But the question now under
consideration is whether the females alone have been modified for this
object. We can see that one sex will not be modified through natural
selection for the sake of protection more than the other, supposing
both to vary, unless one sex is exposed for a longer period to danger,
or has less power of escaping from such danger than the other; and
it does not appear that with fishes the sexes differ in these
respects. As far as there is any difference, the males, from being
generally smaller and from wandering more about, are exposed to
greater danger than the females; and yet, when the sexes differ, the
males are almost always the more conspicuously coloured. The ova are
fertilised immediately after being deposited; and when this process
lasts for several days, as in the case of the salmon,*(3) the
female, during the whole time, is attended by the male. After the
ova are fertilised they are, in most cases, left unprotected by both
parents, so that the males and females, as far as oviposition is
concerned, are equally exposed to danger, and both are equally
important for the production of fertile ova; consequently the more
or less brightly-coloured individuals of either sex would be equally
liable to be destroyed or preserved, and both would have an equal
influence on the colours of their offspring.

  * G. Pouchet, L'Institut., Nov. 1, 1871, p. 134.
  *(2) Proc. Zoolog. Soc., 1865, p. 327, pls. xiv. and xv.
  *(3) Yarrell, British Fishes, vol. ii., p. 11.

  Certain fishes belonging to several families, make nests, and some
of them take care of their young when hatched. Both sexes of the
bright-coloured Crenilabrus massa and melops work together in building
their nests with seaweed, shells, &c.* But the males of certain fishes
do all the work, and afterward take exclusive charge of the young.
This is the case with the dull-coloured gobies,*(2) in which the sexes
are not known to differ in colour, and likewise with the
sticklebacks (Gasterosteus), in which the males become brilliantly
coloured during the spawning season. The male of the smooth-tailed
stickleback (G. leiurus) performs the duties of a nurse with exemplary
care and vigilance during a long time, and is continually employed
in gently leading back the young to the nest, when they stray too far.
He courageously drives away all enemies including the females of his
own species. It would indeed be no small relief to the male, if the
female, after depositing her eggs, were immediately devoured by some
enemy, for he is forced incessantly to drive her from the nest.*(3)

  * According to the observations of M. Gerbe; see Gunther's Record of
Zoolog. Literature, 1865, p. 194.
  *(2) Cuvier, Regne Animal, vol. ii., 1829, p. 242.
  *(3) See Mr. Warington's most interesting description of the
habits of the Gasterosteus leiurus in Annals and Magazine of Nat.
History, November, 1855.

  The males of certain other fishes inhabiting South America and
Ceylon, belonging to two distinct Orders, have the extraordinary habit
of hatching within their mouths, or branchial cavities, the eggs
laid by the females.* I am informed by Professor Agassiz that the
males of the Amazonian species which follow this habit, "not only
are generally brighter than the females, but the difference is greater
at the spawning-season than at any other time." The species of
Geophagus act in the same manner; and in this genus, a conspicuous
protuberance becomes developed on the forehead of the males during the
breeding-season. With the various species of chromids, as Professor
Agassiz likewise informs me, sexual differences in colour may be
observed, "whether they lay their eggs in the water among aquatic
plants, or deposit them in holes, leaving them to come out without
further care, or build shallow nests in the river mud, over which they
sit, as our Pomotis does. It ought also to be observed that these
sitters are among the brightest species in their respective
families; for instance, Hygrogonus is bright green, with large black
ocelli, encircled with the most brilliant red." Whether with all the
species of chromids it is the male alone which sits on the eggs is not
known. It is, however, manifest that the fact of the eggs being
protected or unprotected by the parents, has had little or no
influence on the differences in colour between the sexes. It is
further manifest, in all the cases in which the males take exclusive
charge of the nests and young, that the destruction of the
brighter-coloured males would be far more influential on the character
of the race, than the destruction of the brighter-coloured females;
for the death of the male during the period of incubation or nursing
would entail the death of the young, so that they could not inherit
his peculiarities; yet, in many of these very cases the males are more
conspicuously coloured than the females.

  * Prof. Wyman, in Proc. Boston Soc. of Nat. Hist., Sept. 15, 1857.
Also Prof. Turner, in Journal of Anatomy and Physiology, Nov. 1, 1866,
p. 78. Dr. Gunther has likewise described other cases.

  In most of the Lophobranchii (pipe-fish, Hippocampi, &c.) the
males have either marsupial sacks or hemispherical depressions on
the abdomen, in which the ova laid by the female are hatched. The
males also shew great attachment to their young.* The sexes do not
commonly differ much in colour; but Dr. Gunther believes that the male
Hippocampi are rather brighter than the females. The genus
Solenostoma, however, offers a curious exceptional case,*(2) for the
female is much more vividly-coloured and spotted than the male, and
she alone has a marsupial sack and hatches the eggs; so that the
female of Solenostoma differs from all the other Lophobranchii in this
latter respect, and from almost all other fishes, in being more
brightly-coloured than the male. It is improbable that this remarkable
double inversion of character in the female should be an accidental
coincidence. As the males of several fishes, which take exclusive
charge of the eggs and young, are more brightly coloured than the
females, and as here the female Solenostoma takes the same charge
and is brighter than the male, it might be argued that the conspicuous
colours of that sex which is the more important of the two for the
welfare of the offspring, must be in some manner protective. But
from the large number of fishes, of which the males are either
permanently or periodically brighter than the females, but whose
life is not at all more important for the welfare of the species
than that of the female, this view can hardly be maintained. When we
treat of birds we shall meet with analogous cases, where there has
been a complete inversion of the usual attributes of the two sexes,
and we shall then give what appears to be the probable explanation,
namely, that the males have selected the more attractive females,
instead of the latter having selected, in accordance with the usual
rule throughout the animal kingdom, the more attractive males.

[Bullseye]

* Yarrell, History of British Fishes, vol. ii., 1836, pp. 329, 338.
  *(2) Dr. Gunther, since publishing an account of this species in The
Fishes of Zanzibar, by Col. Playfair, 1866, p. 137, has re-examined
the specimens, and has given me the above information.

  On the whole we may conclude, that with most fishes, in which the
sexes differ in colour or in other ornamental characters, the males
originally varied, with their variations transmitted to the same
sex, and accumulated through sexual selection by attracting or
exciting the females. In many cases, however, such characters have
been transferred, either partially or completely, to the females. In
other cases, again, both sexes have been coloured alike for the sake
of protection; but in no instance does it appear that the female alone
has had her colours or other characters specially modified for this
latter purpose.
  The last point which need be noticed is that fishes are known to
make various noises, some of which are described as being musical. Dr.
Dufosse, who has especially attended to this subject, says that the
sounds are voluntarily produced in several ways by different fishes:
by the friction of the pharyngeal bones- by the vibration of certain
muscles attached to the swim bladder, which serves as a resounding
board- and by the vibration of the intrinsic muscles of the swim
bladder. By this latter means the Trigla produces pure and
long-drawn sounds which range over nearly an octave. But the most
interesting case for us is that of two species of Ophidium, in which
the males alone are provided with a sound-producing apparatus,
consisting of small movable bones, with proper muscles, in
connection with the swim bladder.* The drumming of the Umbrinas in the
European seas is said to be audible from a depth of twenty fathoms;
and the fishermen of Rochelle assert "that the males alone make the
noise during the spawning-time; and that it is possible by imitating
it, to take them without bait."*(2) From this statement, and more
especially from the case of Ophidium, it is almost certain that in
this, the lowest class of the Vertebrata, as with so many insects
and spiders, sound-producing instruments have, at least in some cases,
been developed through sexual selection, as a means for bringing the
sexes together.

  * Comptes-Rendus, tom. xlvi., 1858, p. 353; tom. xlvii., 1858, p.
916; tom. liv., 1862, p. 393. The noise made by the Umbrinas
(Sciaena aquila), is said by some authors to be more like that of a
flute or organ, than drumming: Dr. Zouteveen, in the Dutch translation
of this work (vol. ii., p. 36), gives some further particulars on
the sounds made by fishes.
  *(2) The Rev. C. Kingsley, in Nature, May, 1870, p. 40.

                        AMPHIBIANS.

  URODELA.- I will begin with the tailed amphibians. The sexes of
salamanders or newts often differ much both in colour and structure.
In some species prehensile claws are developed on the fore-legs of the
males during the breeding-season: and at this season in the male
Triton palmipes the hind-feet are provided with a swimming-web,
which is almost completely absorbed during the winter; so that their
feet then resemble those of the female.* This structure no doubt
aids the male in his eager search and pursuit of the female. Whilst
courting her he rapidly vibrates the end of his tail. With our
common newts (Triton punctatus and cristatus) a deep, much indented
crest is developed along the back and tail of the male during the
breeding-season, which disappears during the winter. Mr. St. George
Mivart informs me that it is not furnished with muscles, and therefore
cannot be used for locomotion. As during the season of courtship it
becomes edged with bright colours, there can hardly be a doubt that it
is a masculine ornament. In many species the body presents strongly
contrasted, though lurid tints, and these become more vivid during the
breeding-season. The male, for instance, of our common little newt
(Triton punctatus) is "brownish-grey above, passing into yellow
beneath, which in the spring becomes a rich bright orange, marked
everywhere with round dark spots." The edge of the crest also is
then tipped with bright red or violet. The female is usually of a
yellowish-brown colour with scattered brown dots, and the lower
surface is often quite plain.*(2) The young are obscurely tinted.
The ova are fertilised during the act of deposition, and are not
subsequently tended by either parent. We may therefore conclude that
the males have acquired their strongly-marked colours and ornamental
appendages through sexual selection; these being transmitted either to
the male offspring alone, or to both sexes.

  * Bell, History of British Reptiles, 2nd ed., 1849, pp. 156-159.
  *(2) Bell, History of British Reptiles, 2nd ed., 1849, pp. 146, 151.

  ANURA or BATRACHIA.- With many frogs and toads the colours evidently
serve as a protection, such as the bright green tints of tree frogs
and the obscure mottled shades of many terrestrial species. The most
conspicuously-coloured toad which I ever saw, the Phryniscus
nigricans,* had the whole upper surface of the body as black as ink,
with the soles of the feet and parts of the abdomen spotted with the
brightest vermilion. It crawled about the bare sandy or open grassy
plains of La Plata under a scorching sun, and could not fail to
catch the eye of every passing creature. These colours are probably
beneficial by making this animal known to all birds of prey as a
nauseous mouthful.

  * Zoology of the Voyage of the Beagle, 1843. Bell, ibid., p. 49.

  In Nicaragua there is a little frog "dressed in a bright livery of
red and blue" which does not conceal itself like most other species,
but hops about during the daytime, and Mr. Belt says* that as soon
as he saw its happy sense of security, he felt sure that it was
uneatable. After several trials he succeeded in tempting a young
duck to snatch up a young one, but it was instantly rejected; and
the duck "went about jerking its head, as if trying to throw off
some unpleasant taste."

  * The Naturalist in Nicaragua, 1874, p. 321.

  With respect to sexual differences of colour, Dr. Gunther does not
know of any striking instance either with frogs or toads; yet he can
often distinguish the male from the female by the tints of the
former being a little more intense. Nor does he know of any striking
difference in external structure between the sexes, excepting the
prominences which become developed during the breeding-season on the
front legs of the male, by which he is enabled to hold the female.* It
is surprising that these animals have not acquired more
strongly-marked sexual characters; for though cold-blooded their
passions are strong. Dr. Gunther informs me that he has several
times found an unfortunate female toad dead and smothered from
having been so closely embraced by three or four males. Frogs have
been observed by Professor Hoffman in Giessen fighting all day long
during the breeding-season, and with so much violence that one had its
body ripped open.

  * The male alone of the Bufo sikimmensis (Dr. Anderson, Proc.
Zoolog. Soc., 1871, p. 204) has two plate-like callosities on the
thorax and certain rugosities on the fingers, which perhaps subserve
the same end as the above-mentioned prominences.

  Frogs and toads offer one interesting sexual difference, namely,
in the musical powers possessed by the males; but to speak of music,
when applied to the discordant and overwhelming sounds emitted by male
bullfrogs and some other species, seems, according to our taste, a
singularly inappropriate expression. Nevertheless, certain frogs
sing in a decidedly pleasing manner. Near Rio Janeiro I used often
to sit in the evening to listen to a number of little Hylae, perched
on blades of grass close to the water, which sent forth sweet chirping
notes in harmony. The various sounds are emitted chiefly by the
males during the breeding-season, as in the case of the croaking of
our common frog.* In accordance with this fact the vocal organs of the
males are more highly-developed than those of the females. In some
genera the males alone are provided with sacs which open into the
larynx.*(2) For instance, in the edible frog (Rana esculenta) "the
sacs are peculiar to the males, and become, when filled with air in
the act of croaking, large globular bladders, standing out one on each
side of the head, near the corners of the mouth." The croak of the
male is thus rendered exceedingly powerful; whilst that of the
female is only a slight groaning noise.*(3) In the several genera of
the family the vocal organs differ considerably in structure, and
their development in all cases may be attributed to sexual selection.

  * Bell, History British Reptiles, 1849, p. 93.
  *(2) J. Bishop, in Todd's Cyclopaedia of Anatomy and Physiology,
vol. iv., p. 1503.
  *(3) Bell, ibid., pp. 112-114.

                           REPTILES.

  CHELONIA.- Tortoises and turtles do not offer well-marked sexual
differences. In some species, the tail of the male is longer than that
of the female. In some, the plastron or lower surface of the shell
of the male is slightly concave in relation to the back of the female.
The male of the mud-turtle of the United States (Chrysemys picta)
has claws on its front feet twice as long as those of the female;
and these are used when the sexes unite.* With the huge tortoise of
the Galapagos Islands (Testudo nigra) the males are said to grow to
a larger size than the females: during the pairing-season, and at no
other time, the male utters a hoarse bellowing noise, which can be
heard at the distance of more than a hundred yards; the female, on the
other hand, never uses her voice.*(2)

  * Mr. C. J. Maynard, the American Naturalist, Dec., 1869, p. 555.
  *(2) See my Journal of Researches during the Voyage of the Beagle,
1845, p. 384.

  With the Testudo elegans of India, it is said "that the combats of
the males may be heard at some distance, from the noise they produce
in butting against each other."*

  * Dr. Gunther, Reptiles of British India, 1864, p. 7.

  CROCODILIA.- The sexes apparently do not differ in colour; nor do
I know that the males fight together, though this is probable, for
some kinds make a prodigious display before the females. Bartram*
describes the male alligator as striving to win the female by
splashing and roaring in the midst of a lagoon, "swollen to an
extent ready to burst, with its head and tail lifted up, he springs or
twirls round on the surface of the water, like an Indian chief
rehearsing his feats of war." During the season of love, a musky odour
is emitted by the sub-maxiliary glands of the crocodile, and
pervades their haunts.*(2)

  * Travels through Carolina, &c., 1791, p. 128.
  *(2) Owen, Anatomy of Vertebrates, vol. i., 1866, p. 615.

  OPHIDIA.- Dr. Gunther informs me that the males are always smaller
than the females, and generally have longer and slenderer tails; but
he knows of no other difference in external structure. In regard to
colour, be can almost always distinguish the male from the female,
by his more strongly-pronounced tints; thus the black zigzag band on
the back of the male English viper is more distinctly defined than
in the female. The difference is much plainer in the rattle-snakes
of N. America, the male of which, as the keeper in the Zoological
Gardens shewed me, can at once be distinguished from the female by
having more lurid yellow about its whole body. In S. Africa the
Bucephalus capensis presents an analogous difference, for the female
"is never so fully variegated with yellow on the sides as the
male."* The male of the Indian Dipsas cynodon, on the other hand, is
blackish-brown, with the belly partly black, whilst the female is
reddish or yellowish-olive, with the belly either uniform yellowish or
marbled with black. In the Tragops dispar of the same country the male
is bright green, and the female bronze-coloured.*(2) No doubt the
colours of some snakes are protective, as shewn by the green tints
of tree-snakes, and the various mottled shades of the species which
live in sandy places; but it is doubtful whether the colours of many
kinds, for instance of the common English snake and viper, serve to
conceal them; and this is still more doubtful with the many foreign
species which are coloured with extreme elegance. The colours of
certain species are very different in the adult and young states.*(3)

  * Sir Andrew Smith, Zoology of S. Africa: Reptilia, 1849, pl. x.
  *(2) Dr. A. Gunther, "Reptiles of British India," Ray Soc., 1864,
pp. 304, 308.
  *(3) Dr. Stoliczka, Journal of Asiatic Society of Bengal., vol.
xxxix, 1870, pp. 205, 211.

  During the breeding-season the anal scentglands of snakes are in
active function;* and so it is with the same glands in lizards, and as
we have seen with the submaxiliary glands of crocodiles. As the
males of most animals search for the females, these odoriferous glands
probably serve to excite or charm the female, rather than to guide her
to the spot where the male may be found. Male snakes, though appearing
so sluggish, are amorous; for many have been observed crowding round
the same female, and even round her dead body. They are not known to
fight together from rivalry. Their intellectual powers are higher than
might have been anticipated. In the Zoological Gardens they soon learn
not to strike at the iron bar with which their cages are cleaned;
and Dr. Keen of Philadelphia informs me that some snakes which he kept
learned after four or five times to avoid a noose, with which they
were at first easily caught. An excellent observer in Ceylon, Mr. E.
Layard, saw*(2) a cobra thrust its head through a narrow hole and
swallow a toad. "With this encumbrance be could not withdraw
himself; finding this, he reluctantly disgorged the precious morsel,
which began to move off; this was too much for snake philosophy to
bear, and the toad was again seized, and again was the snake, after
violent efforts to escape, compelled to part with its prey. This time,
however, a lesson had been learnt, and the toad was seized by one leg,
withdrawn, and then swallowed in triumph."

[Bullseye]

* Owen, Anatomy of Vertebrates, vol. i., 1866, p. 615.
  *(2) "Rambles in Ceylon," in Annals and Magazine of Natural History,
2nd series, vol. ix., 1852, p. 333.

  The keeper in the Zoological Gardens is positive that certain
snakes, for instance Crotalus and Python, distinguish him from all
other persons. Cobras kept together in the same cage apparently feel
some attachment towards each other.*

  * Dr. Gunther, Reptiles of British India, 1864, p. 340.

  It does not, however, follow because snakes have some reasoning
power, strong passions and mutual affection, that they should likewise
be endowed with sufficient taste to admire brilliant colours in
their partners, so as to lead to the adornment of the species
through sexual selection. Nevertheless, it is difficult to account
in any other manner for the extreme beauty of certain species; for
instance, of the coral-snakes of S. America, which are of a rich red
with black and yellow transverse bands. I well remember how much
surprise I felt at the beauty of the first coral-snake which I saw
gliding across a path in Brazil. Snakes coloured in this peculiar
manner, as Mr. Wallace states on the authority of Dr. Gunther,* are
found nowhere else in the world except in S. America, and here no less
than four genera occur. One of these, Elaps, is venomous; a second and
widely-distinct genus is doubtfully venomous, and the two others are
quite harmless. The species belonging to these distinct genera inhabit
the same districts, and are so like each other that no one "but a
naturalist would distinguish the harmless from the poisonous kinds."
Hence, as Mr. Wallace believes, the innocuous kinds have probably
acquired their colours as a protection, on the principle of imitation;
for they would naturally be thought dangerous by their enemies. The
cause, however, of the bright colours of the venomous Elaps remains to
be explained, and this may perhaps be sexual selection.

  * Westminster Review, July 1, 1867, p. 32.

  Snakes produce other sounds besides hissing. The deadly Echis
carinata has on its sides some oblique rows of scales of a peculiar
structure with serrated edges; and when this snake is excited these
scales are rubbed against each other, which produces "a curious
prolonged, almost hissing sound."* With respect to the rattling of the
rattle-snake, we have at last some definite information: for Professor
Aughey states,*(2) that on two occasions, being himself unseen, he
watched from a little distance a rattle-snake coiled up with head
erect, which continued to rattle at short intervals for half an
hour: and at last he saw another snake approach, and when they met
they paired. Hence be is satisfied that one of the uses of the
rattle is to bring the sexes together. Unfortunately he did not
ascertain whether it was the male or the female which remained
stationary and called for the other. But it by no means follows from
the above fact that the rattle may not be of use to snakes in other
ways, as a warning to animals which would otherwise attack them. Nor
can I quite disbelieve the several accounts which have appeared of
their thus paralysing their prey with fear. Some other snakes also
make a distinct noise by rapidly vibrating their tails against the
surrounding stalks of plants; and I have myself heard this in the case
of a Trigonocephalus in S. America.

  * Dr. Anderson, Proc. Zoolog. Soc., 1871, p. 196.
  *(2) The American Naturalist, 1873, p. 85.

  LACERTILIA.- The males of some, probably of many kinds of lizards,
fight together from rivalry. Thus the arboreal Anolis cristatellus
of S. America is extremely pugnacious: "During the spring and early
part of the summer, two adult males rarely meet without a contest.
On first seeing one another, they nod their heads up and down three or
four times, and at the same time expanding the frill or pouch
beneath the throat; their eyes glisten with rage, and after waving
their tails from side to side for a few seconds, as if to gather
energy, they dart at each other furiously, rolling over and over,
and holding firmly with their teeth. The conflict generally ends in
one of the combatants losing his tail, which is often devoured by
the victor." The male of this species is considerably larger than
the female;* and this, as far as Dr. Gunther has been able to
ascertain, is the general rule with lizards of all kinds. The male
alone of the Cyrtodactylus rubidus of the Andaman Islands possesses
pre-anal pores; and these pores, judging from analogy, probably
serve to emit an odour.*(2)

  * Mr. N. L. Austen kept these animals alive for a considerable time;
see Land and Water, July, 1867, P. 9.
  *(2) Stoliczka, Journal of the Asiatic Society of Bengal, vol.
xxxiv., 1870, p. 166.

  The sexes often differ greatly in various external characters. The
male of the above-mentioned Anolis is furnished with a crest which
runs along the back and tail, and can be erected at pleasure; but of
this crest the female does not exhibit a trace. In the Indian Cophotis
ceylanica, the female has a dorsal crest, though much less developed
than in the male; and so it is, as Dr. Gunther informs me, with the
females of many iguanas, chameleons, and other lizards. In some
species, however, the crest is equally developed in both sexes, as
in the Iguana tuberculata. In the genus Sitana, the males alone are
furnished with a large throat pouch (see fig. 33), which can be folded
up like a fan, and is coloured blue, black, and red; but these
splendid colours are exhibited only during the pairing-season. The
female does not possess even a rudiment of this appendage. In the
Anolis cristatellus, according to Mr. Austen, the throat pouch,
which is bright red marbled with yellow, is present in the female,
though in a rudimental condition. Again, in certain other lizards,
both sexes are equally well provided with throat pouches. Here we
see with species belonging to the same group, as in so many previous
cases, the same character either confined to the males, or more
largely developed in them than in the females, or again equally
developed in both sexes. The little lizards of the genus Draco,
which glide through the air on their rib-supported parachutes, and
which in the beauty of their colours baffle description, are furnished
with skinny appendages to the throat "like the wattles of gallinaceous
birds." These become erected when the animal is excited. They occur in
both sexes, but are best developed when the male arrives at
maturity, at which age the middle appendage is sometimes twice as long
as the head. Most of the species likewise have a low crest running
along the neck; and this is much more developed in the full-grown
males than in the females or young males.*

  * All the foregoing statements and quotations, in regard to
Cophotis, Sitana and Draco, as well as the following facts in regard
to Ceratophora and Chamaeleon, are from Dr. Gunther himself, or from
his magnificent work on the "Reptiles of British India," Ray Soc.,
1864, pp. 122, 130, 135.

  A Chinese species is said to live in pairs during the spring; "and
if one is caught, the other falls from the tree to the ground, and
allows itself to be captured with impunity"- I presume from despair.*

  * Mr. Swinhoe, Proc. Zoolog. Soc., 1870, p. 240.

   There are other and much more remarkable differences between the
sexes of certain lizards. The male of Ceratophora aspera bears on
the extremity of his snout an appendage half as long as the head. It
is cylindrical, covered with scales, flexible, and apparently
capable of ****: in the female it is quite rudimental. In a second
species of the same genus a terminal scale forms a minute horn on
the summit of the flexible appendage; and in a third species (see C.
stoddartii, fig. 34) the whole appendage is converted into a horn,
which is usually of a white colour, but assumes a purplish tint when
the animal is excited. In the adult male of this latter species the
horn is half an inch in length, but it is of quite minute size in
the female and in the young. These appendages, as Dr. Gunther has
remarked to me, may be compared with the combs of gallinaceous
birds, and apparently serve as ornaments.
  In the genus Chamaeleon we come to the acme of difference between
the sexes. The upper part of the skull of the male C. bifurcus (see
fig. 35), an inhabitant of Madagascar, is produced into two great,
solid, bony projections, covered with scales like the rest of the
head; and of this wonderful modification of structure the female
exhibits only a rudiment. Again, in Chamaeleo owenii (see fig. 36),
from the west coast of Africa, the male bears on his snout and
forehead three curious horns, of which the female has not a trace.
These horns consist of an excrescence of bone covered with a smooth
sheath, forming part of the general integuments of the body, so that
they are identical in structure with those of a bull, goat, or other
sheath-horned ruminant. Although the three horns differ so much in
appearance from the two great prolongations of the skull in C.
bifurcus, we can hardly doubt that they serve the same general purpose
in the economy of these two animals. The first conjecture, which
will occur to every one, is that they are used by the males for
fighting together; and as these animals are very quarrelsome,* this is
probably a correct view. Mr. T. W. Wood also informs me that he once
watched two individuals of C. pumilus fighting violently on the branch
of a tree; they flung their heads about and tried to bite each
other; they then rested for a time and afterwards continued their
battle.

  * Dr. Buchholz, Monatsbericht K. Preuss. Akad., Jan., 1874, p. 78.

  With many lizards the sexes differ slightly in colour, the tints and
stripes of the males being brighter and more distinctly defined than
in the females. This, for instance, is the case with the above
Cophotis and with the Acanthodactylus capensis of S. Africa. In a
Cordylus of the latter country, the male is either much redder or
greener than the female. In the Indian Calotes nigrilabris there is
a still greater difference; the lips also of the male are black,
whilst those of the female are green. In our common little
viviparous lizard (Zootoca vivipara) "the under side of the body and
base of the tail in the male are bright orange, spotted with black; in
the female these parts are pale-greyish-green without spots."* We have
seen that the males alone of Sitana possess a throat-pouch; and this
is splendidly tinted with blue, black, and red. In the Proctotretus
tenuis of Chile the male alone is marked with spots of blue, green,
and coppery-red.*(2) In many cases the males retain the same colours
throughout the year, but in others they become much brighter during
the breeding-season; I may give as an additional instance the
Calotes maria, which at this season has a bright red head, the rest of
the body being green.*(3)

  * Bell, History of British Reptiles, 2nd ed., 1849, p. 40.
  *(2) For Proctotretus, see Zoology of the Voyage of the Beagle;
Reptiles by Mr. Bell, p. 8. For the lizards of S. Africa, see
Zoology of S. Africa: Reptiles, by Sir Andrew Smith, pls. 25 and 39.
For the Indian Calotes, see Reptiles of British India, by Dr. Gunther,
p. 143.
  *(3) Gunther in Proceedings, Zoological Society, 1870, p. 778,
with a coloured figure.

  Both sexes of many species are beautifully coloured exactly alike;
and there is no reason to suppose that such colours are protective. No
doubt with the bright green kinds which live in the midst of
vegetation, this colour serves to conceal them; and in N. Patagonia
I saw a lizard (Proctotretus multimaculatus) which, when frightened,
flattened its body, closed its eyes, and then from its mottled tints
was hardly distinguishable from the surrounding sand. But the bright
colours with which so many lizards are ornamented, as well as their
various curious appendages, were probably acquired by the males as
an attraction, and then transmitted either to their male offspring, or
to both sexes. Sexual selection, indeed, seems to have played almost
as important a part with reptiles as with birds; and the less
conspicuous colours of the females in comparison with the males cannot
be accounted for, as Mr. Wallace believes to be the case with birds,
by the greater exposure of the females to danger during incubation.


--------------------------------------------------------------------------------

[Bullseye]

Chapter XIII - Secondary Sexual Characters of Birds

  SECONDARY sexual characters are more diversified and conspicuous
in birds, though not perhaps entailing more important changes of
structure, than in any other class of animals. I shall, therefore,
treat the subject at considerable length. Male birds sometimes, though
rarely, possess special weapons for fighting with each other. They
charm the female by vocal or instrumental music of the most varied
kinds. They are ornamented by all sorts of combs, wattles,
protuberances, horns, air-distended sacks, top-knots, naked shafts,
plumes and lengthened feathers gracefully springing from all parts
of the body. The beak and naked skin about the head, and the feathers,
are often gorgeously coloured. The males sometimes pay their court
by dancing, or by fantastic antics performed either on the ground or
in the air. In one instance, at least, the male emits a musky odour,
which we may suppose serves to charm or excite the female; for that
excellent observer, Mr. Ramsay,* says of the Australian musk-duck
(Biziura lobata) that "the smell which the male emits during the
summer months is confined to that sex, and in some individuals is
retained throughout the year; I have never, even in the
breeding-season, shot a female which had any smell of musk." So
powerful is this odour during the pairing-season, that it can be
detected long before the bird can be seen.*(2) On the whole, birds
appear to be the most aesthetic of all animals, excepting of course
man, and they have nearly the same taste for the beautiful as we have.
This is shown by our enjoyment of the singing of birds, and by our
women, both civilised and savage, decking their heads with borrowed
plumes, and using gems which are hardly more brilliantly coloured than
the naked skin and wattles of certain birds. In man, however, when
cultivated, the sense of beauty is manifestly a far more complex
feeling, and is associated with various intellectual ideas.

  * Ibis., vol. iii. (new series), 1867, p. 414.
  *(2) Gould, Handbook of the Birds of Australia, 1865, vol. ii., p.
383.

  Before treating of the sexual characters with which we are here more
particularly concerned, I may just allude to certain differences
between the sexes which apparently depend on differences in their
habits of life; for such cases, though common in the lower, are rare
in the higher classes. Two humming-birds belonging to the genus
Eustephanus, which inhabit the island of Juan Fernandez, were long
thought to be specifically distinct, but are now known, as Mr. Gould
informs me, to be the male and female of the same species, and they
differ slightly in the form of the beak. In another genus of
humming-birds (Grypus), the beak of the male is serrated along the
margin and hooked at the extremity, thus differing much from that of
the female. In the Neomorpha of New Zealand, there is, as we have
seen, a still wider difference in the form of the beak in relation
to the manner of feeding of the two sexes. Something of the same
kind has been observed with the goldfinch (Carduelis elegans), for I
am assured by Mr. J. Jenner Weir that the bird-catchers can
distinguish the males by their slightly longer beaks. The flocks of
males are often found feeding on the seeds of the teazle (Dipsacus),
which they can reach with their elongated beaks, whilst the females
more commonly feed on the seeds of the betony or Scrophularia. With
a slight difference of this kind as a foundation, we can see how the
beaks of the two sexes might be made to differ greatly through natural
selection. In some of the above cases, however, it is possible that
the beaks of the males may have been first modified in relation to
their contests with other males; and that this afterwards led to
slightly changed habits of life.

  Law of Battle.- Almost all male birds are extremely pugnacious,
using their beaks, wings, and legs for fighting together. We see
this every spring with our robins and sparrows. The smallest of all
birds, namely the humming-bird, is one of the most quarrelsome. Mr.
Gosse* describes a battle in which a pair seized hold of each
other's beaks, and whirled round and round, till they almost fell to
the ground; and M. Montes de Oca, in speaking or another genus of
humming-bird, says that two males rarely meet without a fierce
aerial encounter: when kept in cages "their fighting has mostly
ended in the splitting of the tongue of one of the two, which then
surely dies from being unable to feed."*(2) With waders, the males
of the common water-hen (Gallinula chloropus) "when pairing, fight
violently for the females: they stand nearly upright in the water
and strike with their feet." Two were seen to be thus engaged for half
an hour, until one got hold of the head of the other, which would have
been killed had not the observer interfered; the female all the time
looking on as a quiet spectator.*(3) Mr. Blyth informs me that the
males of an allied bird (Gallicrex cristatus) are a third larger
than the females, and are so pugnacious during the breeding- season
that they are kept by the natives of eastern Bengal for the sake of
fighting. Various other birds are kept in India for the same
purpose, for instance, the bulbuls (Pycnonotus hoemorrhous) which
"fight with great spirit."*(4)

  * Quoted by Mr. Gould, Introduction to the Trochilidae, 1861, page
29.
  *(2) Gould, ibid., p. 52.
  *(3) W. Thompson, Natural History of Ireland: Birds, vol. ii., 1850,
p. 327.
  *(4) Jerdon, Birds of India, 1863, vol. ii., p. 96.

  The polygamous ruff (see Machetes pugnax, fig. 37) is notorious
for his extreme pugnacity; and in the spring, the males, which are
considerably larger than the females, congregate day after day at a
particular spot, where the females propose to lay their eggs. The
fowlers discover these spots by the turf being trampled somewhat bare.
Here they fight very much like game-cocks, seizing each other with
their beaks and striking with their wings. The great ruff of
feathers round the neck is then erected, and according to Col. Montagu
"sweeps the ground as a shield to defend the more tender parts"; and
this is the only instance known to me in the case of birds of any
structure serving as a shield. The ruff of feathers, however, from its
varied and rich colours probably serves in chief part as an
ornament. Like most pugnacious birds, they seem always ready to fight,
and when closely confined, often kill each other; but Montagu observed
that their pugnacity becomes greater during the spring, when the
long feathers on their necks are fully developed; and at this period
the least movement by any one bird provokes a general battle.* Of
the pugnacity of web-footed birds, two instances will suffice: in
Guiana "bloody fights occur during the breeding-season between the
males of the wild musk-duck (Cairina moschata); and where these fights
have occurred the river is covered for some distance with
feathers."*(2) Birds which seem ill-adapted for fighting engage in
fierce conflicts; thus the stronger males of the pelican drive away
the weaker ones, snapping with their huge beaks and giving heavy blows
with their wings. Male snipe fight together, "tugging and pushing each
other with their bills in the most curious manner imaginable." Some
few birds are believed never to fight; this is the case, according
to Audubon, with one of the woodpeckers of the United States (Picu
sauratus), although "the hens are followed by even half a dozen of
their gay suitors."*(3)

  * Macgillivray, History of British Birds, vol. iv., 1852, pp.
177-181.
  *(2) Sir R. Schomburgk, in Journal of Royal Geographic Society, vol.
xiii., 1843, p. 31.
  *(3) Ornithological Biography, vol. i., p. 191. For pelicans and
snipes, see vol. iii., pp. 138, 477.

[Bullseye]

The males of many birds are larger than the females, and this no
doubt is the result of the advantage gained by the larger and stronger
males over their rivals during many generations. The difference in
size between the two sexes is carried to an extreme point in several
Australian species; thus the male musk-duck (Biziura), and the male
Cincloramphus cruralis (allied to our pipits) are by measurement
actually twice as large as their respective females.* With many
other birds the females are larger than the males; and, as formerly
remarked, the explanation often given, namely, that the females have
most of the work in feeding their young, will not suffice. In some few
cases, as we shall hereafter see, the females apparently have acquired
their greater size and strength for the sake of conquering other
females and obtaining possession of the males.

  * Gould, Handbook of Birds of Australia, vol. i., p. 395; vol.
ii., p. 383.

  The males of many gallinaceous birds, especially of the polygamous
kinds, are furnished with special weapons for fighting with their
rivals, namely spurs, which can be used with fearful effect. It has
been recorded by a trustworthy writer* that in Derbyshire a kite
struck at a game-hen accompanied by her chickens, when the **** rushed
to the rescue, and drove his spur right through the eye and skull of
the aggressor. The spur was with difficulty drawn from the skull,
and as the kite, though dead, retained his grasp, the two birds were
firmly locked together; but the **** when disentangled was very little
injured. The invincible courage of the game-**** is notorious: a
gentleman who long ago witnessed the brutal scene, told me that a bird
had both its legs broken by some accident in the cockpit, and the
owner laid a wager that if the legs could be spliced so that the
bird could stand upright, he would continue fighting. This was
effected on the spot, and the bird fought with undaunted courage until
he received his death-stroke. In Ceylon a closely allied, wild
species, the Gallus stanleyi, is known to fight desperately "in
defence of his seraglio," so that one of the combatants is
frequently found dead.*(2) An Indian partridge (Ortygornis gularis),
the male of which is furnished with strong and sharp spurs, is so
quarrelsome "that the scars of former fights disfigure the breast of
almost every bird you kill."*(3)

  * Mr. Hewitt, in the Poultry Book, by Tegetmeier, 1866, p. 137.
  *(2) Layard, Annals and Magazine of Natural History, vol. xiv.,
1854, p. 63.
  *(3) Jerdon, Birds of India, vol. iii., p. 574.

  The males of almost all gallinaceous birds, even those which are not
furnished with spurs, engage during the breeding- season in fierce
conflicts. The capercailzie and black-**** (Tetrao urogallus and T.
tetrix), which are both polygamists, have regular appointed places,
where during many weeks they congregate in numbers to fight together
and to display their charms before the females. Dr. W. Kovalevsky
informs me that in Russia he has seen the snow all bloody on the
arenas where the capercailzie have fought; and the black-cocks "make
the feathers fly in every direction," when several "engage in a battle
royal." The elder Brehm gives a curious account of the balz, as the
love-dances and love songs of the black-**** are called in Germany.
The bird utters almost continuously the strangest noises: "he holds
his tail up and spreads it out like a fan, he lifts up his head and
neck with all the feathers erect, and stretches his wings from the
body. Then he takes a few jumps in different directions sometimes in a
circle, and presses the under part of his beak so hard against the
ground that the chin feathers are rubbed off. During these movements
he beats his wings and turns round and round. The more ardent he grows
the more lively he becomes, until at last the bird appears like a
frantic creature." At such times the black-cocks are so absorbed
that they become almost blind and deaf, but less so than the
capercailzie: hence bird after bird may be shot on the same spot, or
even caught by the hand. After performing these antics the males begin
to fight: and the same black-****, in order to prove his strength over
several antagonists, will visit in the course of one morning several
balz places, which remain the same during successive years.*

  * Brehm, Illust. Thierleben, 1867, B. iv., s. 351. Some of the
foregoing statements are taken from L. Lloyd, Game Birds of Sweden,
&c., 1867, p. 79.

  The peacock with his long train appears more like a dandy than a
warrior, but he sometimes engages in fierce contests: the Rev. W.
Darwin Fox informs me that at some little distance from Chester two
peacocks became so excited whilst fighting, that they flew over the
whole city, still engaged, until they alighted on the top of St.
John's tower.
  The spur, in those gallinaceous birds which are thus provided, is
generally single; but Polyplectron (see fig. 51) has two or more on
each leg; and one of the blood-pheasants (Ithaginis cruentus) has been
seen with five spurs. The spurs are generally confined to the male,
being represented by mere knobs or rudiments in the female; but the
females of the Java peacock (Pavo muticus) and, as I am informed by
Mr. Blyth, of the small fire-backed pheasant (Euplocamus
erythropthalmus) possess spurs. In Galloperdix it is usual for the
males to have two spurs, and for the females to have only one on
each leg.* Hence spurs may be considered as a masculine structure,
which has been occasionally more or less transferred to the females.
Like most other secondary sexual characters, the spurs are highly
variable, both in number and development, in the same species.

  * Jerdon, Birds of India: on Ithaginis, vol. iii., p. 523; on
Galloperdix, p. 541.