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Descent of Man [ 1871]

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« Reply #120 on: February 09, 2009, 03:10:40 pm »

* 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.


  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.


  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."
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