<p>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. (38.
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.) 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.</p>
<p>In most of the Lophobranchii (Pipe-fish, Hippocampi, etc.) 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. (39. Yarrell, ‘History of British Fishes,’ vol. ii.
1836, pp. 329, 338.) 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 (40. 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.), 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.</p>
<p>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.</p>
<p>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. (41.
‘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.) 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.” (42. The Rev. C. Kingsley, in
‘Nature,’ May 1870, p. 40.) 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.</p>
<h3>AMPHIBIANS.</h3> <h3>URODELA.</h3>
<p>[Fig. 32. Triton cristatus (half natural size, from Bell’s ‘British
Reptiles’). Upper figure, male during the breeding season; lower figure,
female.]</p>
<p>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. (43. Bell, ‘History of
British Reptiles,’ 2nd ed., 1849, pp. 156-159.) 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. (44. Bell, ‘History of
British Reptiles,’ 2nd ed., 1849, pp. 146, 151.) 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.</p>
<h3>ANURA OR BATRACHIA.</h3>
<p>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 (45. ‘Zoology of the Voyage of the
“Beagle,”’ 1843. Bell, ibid. p. 49.), 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.</p>
<p>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 (46. ‘The Naturalist in
Nicaragua,’ 1874, p. 321.) 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.”</p>
<p>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. (47. 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.) 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.</p>
<p>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 bull-frogs 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.
(48. Bell, ‘History British Reptiles,’ 1849, p. 93.) 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. (49. J. Bishop, in ‘Todd’s Cyclopaedia
of Anatomy and Physiology,’ vol. iv. p. 1503.) 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. (50. Bell, ibid. pp.
112-114.) 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.</p>
<h3>REPTILES.</h3> <h3>CHELONIA.</h3>
<p>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. (51. Mr. C.J. Maynard,
‘The American Naturalist,’ Dec. 1869, p. 555.) 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. (52. See my ‘Journal of Researches during the Voyage of
the “Beagle,”’ 1845, p. 384.)</p>
<p>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.” (53. Dr. Gunther, ‘Reptiles of British
India,’ 1864, p. 7.)</p>
<h3>CROCODILIA.</h3>
<p>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 (54. ‘Travels through
Carolina,’ etc., 1791, p. 128.) 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 submaxillary glands of the crocodile, and pervades their haunts.
(55. Owen, ‘Anatomy of Vertebrates,’ vol. i. 1866, p. 615.)</p>
<h3>OPHIDIA.</h3>
<p>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.” (56. Sir Andrew Smith, ‘Zoology of S.
Africa: Reptilia,’ 1849, pl. x.) 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. (57. Dr. A. Gunther,
‘Reptiles of British India,’ Ray Soc., 1864, pp. 304, 308.) 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. (58. Dr. Stoliczka, ‘Journal of Asiatic Society of
Bengal,’ vol. xxxix, 1870, pp. 205, 211.)</p>
<p>During the breeding-season the anal scent-glands of snakes are in active
function (59. Owen, ‘Anatomy of Vertebrates,’ vol. i. 1866, p.
615.); and so it is with the same glands in lizards, and as we have seen with
the submaxillary 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 (60. ‘Rambles in
Ceylon,’ in ‘Annals and Magazine of Natural History,’ 2nd
series, vol. ix. 1852, p. 333.) a cobra thrust its head through a narrow hole
and swallow a toad. “With this encumbrance he 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.”</p>
<p>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. (61. Dr. Gunther, ‘Reptiles of British India,’ 1864, p.
340.)</p>
<p>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 (62. ‘Westminster Review,’ July 1st,
1867, p. 32.), 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.</p>
<p>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.”
(63. Dr. Anderson, ‘Proc. Zoolog. Soc.’ 1871, p. 196.) With respect
to the rattling of the rattle-snake, we have at last some definite information:
for Professor Aughey states (64. The ‘American Naturalist,’ 1873,
p. 85.), 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 he 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 these 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.</p>
<h3>LACERTILIA.</h3>
<p>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 (65. Mr. N.L. Austen kept these
animals alive for a considerable time; see ‘Land and Water,’ July
1867, p. 9.); 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. (66. Stoliczka,
‘Journal of the Asiatic Society of Bengal,’ vol. xxxiv. 1870, p.
166.)</p>
<p>[Fig.33. Sitana minor. Male with the gular pouch expanded (from Gunther’s
‘Reptiles of India’)’]</p>
<p>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 (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. (67. 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.)</p>
<p>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. (68. Mr. Swinhoe,
‘Proc. Zoolog. Soc.’ 1870, p. 240.)</p>
<p>[Fig. 34. Ceratophora Stoddartii. Upper figure; lower figure, female.]</p>
<p>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 erection: 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 (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.</p>
<p>[Fig. 35. Chamaeleo bifurcus. Upper figure, male; lower figure, female.</p>
<p>Fig. 36. Chamaeleo Owenii. Upper figure, male; lower figure, female.]</p>
<p>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 (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 (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 (69. Dr. Buchholz,
‘Monatsbericht K. Preuss. Akad.’ Jan. 1874, p. 78.), 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.</p>
<p>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.” (70. Bell, ‘History of British
Reptiles,’ 2nd ed., 1849, p. 40.) 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. (71. 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, pl. 25 and 39. For the Indian Calotes,
see ‘Reptiles of British India,’ by Dr. Gunther, p. 143.) 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. (72. Gunther in ‘Proceedings, Zoological
Society,’ 1870, p. 778, with a coloured figure.)</p>
<p>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 alone, 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.</p>
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