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Descent of Man [ 1871]

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Bullseye
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« Reply #120 on: February 09, 2009, 03:11:00 pm »

* 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.


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