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Chapter XII
SECONDARY SEXUAL CHARACTERS OF FISHES, AMPHIBIANS, AND REPTILES.
FISHES: Courtship and battles of the males--Larger size of the females--
Males, bright colours and ornamental appendages; other strange characters--
Colours and appendages acquired by the males during the breeding-season
alone--Fishes with both sexes brilliantly coloured--Protective colours--The
less conspicuous colours of the female cannot be accounted for on the
principle of protection--Male fishes building nests, and taking charge of
the ova and young.
AMPHIBIANS: Differences in structure and colour between the sexes--Vocal
organs.
REPTILES: Chelonians--Crocodiles--Snakes, colours in some cases
protective--Lizards, battles of--Ornamental appendages--Strange differences
in structure between the sexes--Colours--Sexual differences almost as great
as with birds.
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. (1.
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. (2. The
'American Naturalist,' April 1871, p. 119.) 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 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."
(3. See Mr. R. Warington's interesting articles in 'Annals and Magazine of
Natural History,' October 1852, and November 1855.) The males are said to
be polygamists (4. Noel Humphreys, 'River Gardens,' 1857.); 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 (5. Loudon's 'Magazine of
Natural History,' vol. iii. 1830, p. 331.), "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."
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." (6. The 'Field,' June
29, 1867. For Mr. Shaw's Statement, 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.) 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.
[Fig. 27. Head of male common salmon (Salmo salar) during the breeding-
season.
[This drawing, as well as all the others in the present chapter, have been
executed by the well-known artist, Mr. G. Ford, from specimens in the
British Museum, under the kind superintendence of Dr. Gunther.]
Fig. 28. Head of female salmon.]
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." (7. Yarrell, 'History of British Fishes,' vol. ii. 1836, p.
10.) (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 (8. 'The Naturalist in Vancouver's Island,' vol.
i. 1866, p. 54.) 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 (9. 'Scandinavian Adventures,'
vol. i. 1854, pp. 100, 104.), 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.
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. (10. 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.) 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.
In regard to size, M. Carbonnier (11. As quoted in 'The Farmer,' 1868, p.
369.) 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.
[Fig. 29. Callionymus lyra.
Upper figure, male;
lower figure, female.
N.B. The lower figure is more reduced than the upper.]
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 (12. I have drawn up this description from Yarrell's 'British
Fishes,' vol. i. 1836, pp. 261 and 266.); but the most striking difference
is the extraordinary elongation in the male (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." (13.
'Nature,' July 1873, p. 264.) The young males resemble the adult females
in structure and colour. Throughout the genus Callionymus (14. 'Catalogue
of Acanth. Fishes in the British Museum,' by Dr. Gunther, 1861, pp. 138-
151.), 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.
The male of the Cottus scorpius, or sea-scorpion, is slenderer and smaller
than the female. There is also a great difference in colour between them.
It is difficult, as Mr. Lloyd (15. 'Game Birds of Sweden,' etc., 1867, p.
466.) 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.
[Fig. 30. Xiphophorus Hellerii.
Upper figure, male;
lower figure, female.]
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 (16. 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.), 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
(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. (17. Dr. Gunther makes this
remark; 'Catalogue of Fishes in the British Museum,' vol. iii. 1861, p.
141.)
[Fig.31. Plecostomus barbatus.
Upper figure, head of male;
lower figure, female.]
In a siluroid fish, inhabiting the fresh waters of South America, the
Plecostomus barbatus (18. See Dr. Gunther on this genus, in 'Proceedings
of the Zoological Society,' 1868, p. 232.) (Fig. 31), the male has its
mouth and inter-operculum 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, it 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. (19. 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
(20. Dr. Gunther, 'Catalogue of Fishes,' vol. iii. pp. 221 and 240.), 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 (21. See
also 'A Journey in Brazil,' by Prof. and Mrs. Agassiz, 1868, p. 220.), 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.
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." (22. Yarrell, 'History of British
Fishes,' vol. ii. 1836, pp. 10, 12, 35.) 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. (23. W. Thompson, in 'Annals and Magazine of Natural
History,' vol. vi. 1841, p. 440.) 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. (24.
'The American Agriculturalist,' 1868, p. 100.) Another striking instance
out of many is afforded by the male stickleback (Gasterosteus leiurus),
which is described by Mr. Warington (25. 'Annals and Mag. of Nat. Hist.'
Oct. 1852.), 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.
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." (26. '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. (27. 'Bulletin de la Societe d'Acclimat.'
Paris, July 1869, and Jan. 1870.) 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.
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 (28. Bory Saint Vincent, in 'Dict.
Class. d'Hist. Nat.' tom. ix. 1826, p. 151.), 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. (29. 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.") 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.
What, then, are we to conclude in regard to the many fishes, both sexes of
which are splendidly coloured? Mr. Wallace (30. 'Westminster Review,'
July 1867, p. 7.) 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." (31.
'Indian Cyprinidae,' by Mr. M'Clelland, 'Asiatic Researches,' vol. xix.
part ii. 1839, p. 230.) 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.
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. (32. G. Pouchet, 'L'Institut.' Nov. 1, 1871, p.
134.) 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 (33.
'Proc. Zoolog. Soc.' 1865, p. 327, pl. xiv. and xv.) 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 (34.
Yarrell, 'British Fishes,' vol. ii. p. 11.), 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.
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
sea-weed, shells, etc. (35. According to the observations of M. Gerbe;
see Gunther's 'Record of Zoolog. Literature,' 1865, p. 194.) But the males
of certain fishes do all the work, and afterwards take exclusive charge of
the young. This is the case with the dull-coloured gobies (36. Cuvier,
'Regne Animal,' vol. ii. 1829, p. 242.), 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.
(37. 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.
(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.
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.
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. (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.
AMPHIBIANS.
URODELA.
[Fig. 32. Triton cristatus (half natural size, from Bell's 'British
Reptiles').
Upper figure, male during the breeding season;
lower figure, female.]
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.
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 (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.
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."
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.
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.
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. (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.)
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.)
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 (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 submaxiliary glands of the crocodile, and pervades their haunts. (55.
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." (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.)
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
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 (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."
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.)
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.
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.
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 (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.)
[Fig.33. Sitana minor.
Male with the gular pouch expanded (from Gunther's 'Reptiles of India')']
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.)
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.)
[Fig. 34. Ceratophora Stoddartii.
Upper figure;
lower figure, female.]
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.
[Fig. 35. Chamaeleo bifurcus.
Upper figure, male;
lower figure, female.
Fig. 36. Chamaeleo Owenii.
Upper figure, male;
lower figure, female.]
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.
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 C
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