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Descent of Man [ 1871]

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Bullseye
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« Reply #120 on: February 09, 2009, 03:09:34 pm »

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.

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