WE have now
arrived at the great sub-kingdom
of the Vertebrata,
and will commence with the lowest
class, that of fishes. The males
of plagiostomous fishes (sharks,
rays) and of chimaeroid fishes
are provided with claspers which
serve to retain the female, like
the various structures possessed
by many of the lower animals.
Besides the claspers, the males
of many rays have clusters of
strong sharp spines on their
heads, and several rows along "the
upper outer surface of their
pectoral fins." These are present
in the males of some species,
which have other parts of their
bodies smooth. They are only
temporarily developed during
the breeding-season; and Dr.
Gunther suspects that they are
brought into action as prehensile
organs by the doubling inwards
and downwards of the two sides
of the body. It is a remarkable
fact that the females and not
the males of some species, as
of Raia clavata, have their backs
studded with large hook-formed
spines.*
* Yarrell's Hist. of British
Fishes, vol. ii., 1836, pp 417,
425, 436. Dr. Gunther informs
me that the spines in R. clavata
are peculiar to the female.
The males alone of the capelin
(Mallotus villosus, one of Salmonidae),
are provided with a ridge of
closely-set, brush-like scales,
by the aid of which two males,
one on each side, hold the female,
whilst she runs with great swiftness
on the sandy beach, and there
deposits her spawn.* The widely
distinct Monacanthus scopas presents
a somewhat analogous structure.
The male, as Dr. Gunther informs
me, has a cluster of stiff, straight
spines, like those of a comb,
on the sides of the tail; and
these in a specimen six inches
long were nearly one and a half
inches in length; the female
has in the same place a cluster
of bristles, which may be compared
with those of a tooth-brush.
In another species, M. peronii,
the male has a brush like that
possessed by the female of the
last species, whilst the sides
of the tail in the female are
smooth. In some other species
of the same genus the tail can
be perceived to be a little roughened
in the male and perfectly smooth
in the female; and lastly in
others, both sexes have smooth
sides.
* The American Naturalist, April,
1871, p. 119.
The males of
many fish fight for the possession
of the females.
Thus the male stickleback (Gasterosteus
leiurus) has been described as "mad
with delight," when the female
comes out of her hiding-place
and surveys the nest which he
has made for her. "He darts round
her in every direction, then
to his accumulated materials
for the nest, then back again
in an instant; and as she does
not advance he endeavours to
push her with his snout, and
then tries to pull her by the
tail and side-spine to the nest."*
The males are said to be polygamists;*(2)
they are extraordinarily bold
and pugnacious, whilst "the females
are quite pacific." Their battles
are at times desperate; "for
these puny combatants fasten
tight on each other for several
seconds, tumbling over and over
again until their strength appears
completely exhausted." With the
rough-tailed stickleback (G.
trachurus) the males whilst fighting
swim round and round each other,
biting and endeavouring to pierce
each other with their raised
lateral spines. The same writer
adds,*(3) "the bite of these
little furies is very severe.
They also use their lateral spines
with such fatal effect, that
I have seen one during a battle
absolutely rip his opponent quite
open, so that he sank to the
bottom and died." When a fish
is conquered, "his gallant bearing
forsakes him; his gay colours
fade away; and he hides his disgrace
among his peaceable companions,
but is for some time the constant
object of his conqueror's persecution."
* See Mr, R. Warington's interesting
articles in Annals and Magazine
of Natural History, October,
1852, and November, 1855.
*(2) Noel Humphreys. River Gardens,
1857.
*(3) Loudon's Magazine of Natural
History, vol. iii., 1830, p.
331.
The male salmon
is as pugnacious as the little
stickleback; and
so is the male trout, as I hear
from Dr. Gunther. Mr. Shaw saw
a violent contest between two
male salmon which lasted the
whole day; and Mr. R. Buist,
Superintendent of Fisheries,
informs me that he has often
watched from the bridge at Perth
the males driving away their
rivals, whilst the females were
spawning The males "are constantly
fighting and tearing each other
on the spawning-beds, and many
so injure each other as to cause
the death of numbers, many being
seen swimming near the banks
of the river in a state of exhaustion,
and apparently in a dying state."*
Mr. Buist informs me, that in
June 1868, the keeper of the
Stormontfield breeding-ponds
visited the northern Tyne and
found about 300 dead salmon,
all of which with one exception
were males; and he was convinced
that they had lost their lives
by fighting.
* The Field, June 29, 1867.
For Mr. Shaw's statements, see
Edinburgh Review, 1843. Another
experienced observer (Scrope's
Days of Salmon Fishing, p. 60)
remarks that like the stag, the
male would, if he could, keep
all other males away.
The most curious
point about the male salmon
is that during
the breeding-season, besides
a slight change in colour, "the
lower jaw elongates, and a cartilaginous
projection turns upwards from
the point, which, when the jaws
are closed, occupies a deep cavity
between the intermaxillary bones
of the upper jaw."* (See figs.
27 and 28.) In our salmon this
change of structure lasts only
during the breeding-season; but
in the Salmo lycaodon of N. W.
America the change, as Mr. J.
K. Lord*(2) believes, is permanent,
and best marked in the older
males which have previously ascended
the rivers. In these old males
the jaw becomes developed into
an immense hook-like projection,
and the teeth grow into regular
fangs, often more than half an
inch in length. With the European
salmon, according to Mr. Lloyd,*(3)
the temporary hook-like structure
serves to strengthen and protect
the jaws, when one male charges
another with wonderful violence;
but the greatly developed teeth
of the male American salmon may
be compared with the tusks of
many male mammals, and they indicate
an offensive rather than a protective
purpose.
* Yarrell, History of British
Fishes, vol. ii., 1836, p. 10.
*(2) The Naturalist in Vancouver's
Island, vol. i., 1866, p. 54.
*(3) Scandinavian Adventures,
vol. i., 1854, pp. 100, 104.
The salmon is not the only fish
in which the teeth differ in
the two sexes; as this is the
case with many rays. In the thornback
(Raia clavata) the adult male
has sharp, pointed teeth, directed
backwards, whilst those of the
female are broad and flat, and
form a pavement; so that these
teeth differ in the two sexes
of the same species more than
is usual in distinct genera of
the same family. The teeth of
the male become sharp only when
he is adult: whilst young they
are broad and flat like those
of the female. As so frequently
occurs with secondary sexual
characters, both sexes of some
species of rays (for instance
R. batis), when adult, possess
sharp pointed teeth; and here
a character, proper to and primarily
gained by the male, appears to
have been transmitted to the
offspring of both sexes. The
teeth are likewise pointed in
both sexes of R. maculata, but
only when quite adult; the males
acquiring them at an earlier
age than the females. We shall
hereafter meet with analogous
cases in certain birds, in which
the male acquires the plumage
common to both sexes when adult,
at a somewhat earlier age than
does the female. With other species
of rays the males even when old
never possess sharp teeth, and
consequently the adults of both
sexes are provided with broad,
flat teeth like those of the
young, and like those of the
mature females of the above-mentioned
species.* As the rays are bold,
strong and voracious fish, we
may suspect that the males require
their sharp teeth for fighting
with their rivals; but as they
possess many parts modified and
adapted for the prehension of
the female, it is possible that
their teeth may be used for this
purpose.
* See Yarrell's account of the
rays in his History of British
Fishes, vol. ii., 1836, p. 416,
with an excellent figure, and
pp. 422, 432.
In regard to size, M. Carbonnier*
maintains that the female of
almost all fishes is larger than
the male; and Dr. Gunther does
not know of a single instance
in which the male is actually
larger than the female. With
some cyprinodonts the male is
not even half as large. As in
many kinds of fishes the males
habitually fight together, it
is surprising that they have
not generally become larger and
stronger than the females through
the effects of sexual selection.
The males suffer from their small
size, for according to M. Carbonnier,
they are liable to be devoured
by the females of their own species
when carnivorous, and no doubt
by other species. Increased size
must be in some manner of more
importance to the females, than
strength and size are to the
males for fighting with other
males; and this perhaps is to
allow of the production of a
vast number of ova.
* As quoted in the Farmer, 1868,
p. 369.
In many species
the male alone is ornamented
with bright colours;
or these are much brighter in
the male than the female. The
male, also, is sometimes provided
with appendages which appear
to be of no more use to him for
the ordinary purposes of life,
than are the tail feathers to
the peacock. I am indebted for
most of the following facts to
the kindness of Dr. Gunther.
There is reason to suspect that
many tropical fishes differ sexually
in colour and structure; and
there are some striking cases
with our British fishes. The
male Callionymus lyra has been
called the gemmeous dragonet "from
its brilliant gem-like colours." When
fresh caught from the sea the
body is yellow of various shades,
striped and spotted with vivid
blue on the head; the dorsal
fins are pale brown with dark
longitudinal bands; the ventral,
caudal, and anal fins being bluish-black.
The female, or sordid dragonet,
was considered by Linnaeus, and
by many subsequent naturalists,
as a distinct species; it is
of a dingy reddish-brown, with
the dorsal fin brown and the
other fins white. The sexes differ
also in the proportional size
of the head and mouth, and in
the position of the eyes;* but
the most striking difference
is the extraordinary elongation
in the male (see fig. 29) of
the dorsal fin. Mr. W. Saville
Kent remarks that this "singular
appendage appears from my observations
of the species in confinement,
to be subservient to the same
end as the wattles, crests, and
other abnormal adjuncts of the
male in gallinaceous birds, for
the purpose of fascinating their
mates."*(2) The young males resemble
the adult females in structure
and colour. Throughout the genus
Callionymus,*(3) the male is
generally much more brightly
spotted than the female, and
in several species, not only
the dorsal, but the anal fin
is much elongated in the males.
* I have drawn up this description
from Yarrell's British Fishes,
vol. i., 1836, pp. 261 and 266.
*(2) Nature, July, 1873, p.
264.
*(3) Catalogue of Acanth. Fishes
in the British Museum, by Dr.
Gunther, 1861, pp. 138-151.
The male of
the Cottus scorpius, or sea-serpent,
is slenderer
and smaller than the female.
There is also a great difference
in colour between them. It is
difficult, as Mr. Lloyd* remarks, "for
any one, who has not seen this
fish during the spawning-season,
when its hues are brightest,
to conceive the admixture of
brilliant colours with which
it, in other respects so ill-favoured,
is at that time adorned. Both
sexes of the Labrus mixtus, although
very different in colour, are
beautiful; the male being orange
with bright blue stripes, and
the female bright red with some
black spots on the back.
* Game Birds
of Sweden, &c.,
1867, p. 466.
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,*
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 (see 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.*(2)
* 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.
*(2) Dr. Gunther makes this
remark, Catalogue of Fishes in
the British Museum, vol. iii.,
1861, p. 141.
In a siluroid
fish, inhabiting the fresh
waters of South America,
the Plecostomus barbatus* (see
fig. 31), the male has its mouth
and interoperculum 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, 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.*(2)
* See Dr. Gunther on this genus,
in Proceedings of the Zoological
Society, 1868, p. 232.
*(2) 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,* 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,*(2) 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.
* Dr. Gunther, Catalogue of
Fishes, vol. iii., pp. 221 and
240.
*(2) See also A Journey in Brazil,
by Prof. and Mrs. Agassiz, 1868,
p. 220.
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."*
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.*(2)
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.*(3)
Another striking instance out
of many is afforded by the male
stickleback (Gasterosteus leiurus),
which is described by Mr. Warington,*(4)
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.
* Yarrell, History of British
Fishes, vol. ii., 1836, pp. 10,
12, 35.
*(2) W. Thompson, in Annals
and Magazine of Natural History,
vol. vi., 1841, p. 440.
*(3) The American Agriculturalist,
1868, p. 100.
*(4) Annals and Mag. of Nat.
Hist., Oct., 1852.
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."*
* 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.* 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.
* Bulletin de la Societe d'Acclimation,
Paris, July, 1869, and Jan.,
1870.
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,*
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.*(2)
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.
* Bory de Saint Vincent, in
Dict. Class. d'Hist. Nat., tom.
ix., 1826, p. 151.
*(2) 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."
What, then,
are we to conclude in regard
to the many fishes,
both sexes of which are splendidly
coloured? Mr. Wallace* 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."*(2) 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.
* Westminster Review, July,
1867, p. 7.
*(2) "Indian Cyprinidae," by
Mr. M'Clelland, Asiatic Researches,
vol. xix., part ii., 1839, p.
230.
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.*
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*(2)
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,*(3)
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.
* G. Pouchet, L'Institut., Nov.
1, 1871, p. 134.
*(2) Proc. Zoolog. Soc., 1865,
p. 327, pls. xiv. and xv.
*(3) Yarrell, British Fishes,
vol. ii., p. 11.
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 seaweed, shells, &c.*
But the males of certain fishes
do all the work, and afterward
take exclusive charge of the
young. This is the case with
the dull-coloured gobies,*(2)
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.*(3)
* According to the observations
of M. Gerbe; see Gunther's Record
of Zoolog. Literature, 1865,
p. 194.
*(2) Cuvier, Regne Animal, vol.
ii., 1829, p. 242.
*(3) 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.*
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.
* 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.
In most of the
Lophobranchii (pipe-fish, Hippocampi, &c.)
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.* 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,*(2)
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.
* Yarrell, History of British
Fishes, vol. ii., 1836, pp. 329,
338.
*(2) Dr. Gunther, since publishing
an account of this species in
The Fishes of Zanzibar, by Col.
Playfair, 1866, p. 137, has re-examined
the specimens, and has given
me the above information.
On the whole we may conclude,
that with most fishes, in which
the sexes differ in colour or
in other ornamental characters,
the males originally varied,
with their variations transmitted
to the same sex, and accumulated
through sexual selection by attracting
or exciting the females. In many
cases, however, such characters
have been transferred, either
partially or completely, to the
females. In other cases, again,
both sexes have been coloured
alike for the sake of protection;
but in no instance does it appear
that the female alone has had
her colours or other characters
specially modified for this latter
purpose.
The last point
which need be noticed is that
fishes are known
to make various noises, some
of which are described as being
musical. Dr. Dufosse, who has
especially attended to this subject,
says that the sounds are voluntarily
produced in several ways by different
fishes: by the friction of the
pharyngeal bones- by the vibration
of certain muscles attached to
the swim bladder, which serves
as a resounding board- and by
the vibration of the intrinsic
muscles of the swim bladder.
By this latter means the Trigla
produces pure and long-drawn
sounds which range over nearly
an octave. But the most interesting
case for us is that of two species
of Ophidium, in which the males
alone are provided with a sound-producing
apparatus, consisting of small
movable bones, with proper muscles,
in connection with the swim bladder.*
The drumming of the Umbrinas
in the European seas is said
to be audible from a depth of
twenty fathoms; and the fishermen
of Rochelle assert "that the
males alone make the noise during
the spawning-time; and that it
is possible by imitating it,
to take them without bait."*(2)
From this statement, and more
especially from the case of Ophidium,
it is almost certain that in
this, the lowest class of the
Vertebrata, as with so many insects
and spiders, sound-producing
instruments have, at least in
some cases, been developed through
sexual selection, as a means
for bringing the sexes together.
* Comptes-Rendus, tom. xlvi.,
1858, p. 353; tom. xlvii., 1858,
p. 916; tom. liv., 1862, p. 393.
The noise made by the Umbrinas
(Sciaena aquila), is said by
some authors to be more like
that of a flute or organ, than
drumming: Dr. Zouteveen, in the
Dutch translation of this work
(vol. ii., p. 36), gives some
further particulars on the sounds
made by fishes.
*(2) The Rev. C. Kingsley, in
Nature, May, 1870, p. 40.
AMPHIBIANS.
URODELA.- I
will begin with the tailed
amphibians. The sexes
of salamanders or newts often
differ much both in colour and
structure. In some species prehensile
claws are developed on the fore-legs
of the males during the breeding-season:
and at this season in the male
Triton palmipes the hind-feet
are provided with a swimming-web,
which is almost completely absorbed
during the winter; so that their
feet then resemble those of the
female.* This structure no doubt
aids the male in his eager search
and pursuit of the female. Whilst
courting her he rapidly vibrates
the end of his tail. With our
common newts (Triton punctatus
and cristatus) a deep, much indented
crest is developed along the
back and tail of the male during
the breeding-season, which disappears
during the winter. Mr. St. George
Mivart informs me that it is
not furnished with muscles, and
therefore cannot be used for
locomotion. As during the season
of courtship it becomes edged
with bright colours, there can
hardly be a doubt that it is
a masculine ornament. In many
species the body presents strongly
contrasted, though lurid tints,
and these become more vivid during
the breeding-season. The male,
for instance, of our common little
newt (Triton punctatus) is "brownish-grey
above, passing into yellow beneath,
which in the spring becomes a
rich bright orange, marked everywhere
with round dark spots." The edge
of the crest also is then tipped
with bright red or violet. The
female is usually of a yellowish-brown
colour with scattered brown dots,
and the lower surface is often
quite plain.*(2) The young are
obscurely tinted. The ova are
fertilised during the act of
deposition, and are not subsequently
tended by either parent. We may
therefore conclude that the males
have acquired their strongly-marked
colours and ornamental appendages
through sexual selection; these
being transmitted either to the
male offspring alone, or to both
sexes.
* Bell, History of British Reptiles,
2nd ed., 1849, pp. 156-159.
*(2) Bell, History of British
Reptiles, 2nd ed., 1849, pp.
146, 151.
ANURA or BATRACHIA.- With many
frogs and toads the colours evidently
serve as a protection, such as
the bright green tints of tree
frogs and the obscure mottled
shades of many terrestrial species.
The most conspicuously-coloured
toad which I ever saw, the Phryniscus
nigricans,* had the whole upper
surface of the body as black
as ink, with the soles of the
feet and parts of the abdomen
spotted with the brightest vermilion.
It crawled about the bare sandy
or open grassy plains of La Plata
under a scorching sun, and could
not fail to catch the eye of
every passing creature. These
colours are probably beneficial
by making this animal known to
all birds of prey as a nauseous
mouthful.
* Zoology of the Voyage of the
Beagle, 1843. Bell, ibid., p.
49.
In Nicaragua
there is a little frog "dressed in a bright livery
of red and blue" which does not
conceal itself like most other
species, but hops about during
the daytime, and Mr. Belt says*
that as soon as he saw its happy
sense of security, he felt sure
that it was uneatable. After
several trials he succeeded in
tempting a young duck to snatch
up a young one, but it was instantly
rejected; and the duck "went
about jerking its head, as if
trying to throw off some unpleasant
taste."
* The Naturalist in Nicaragua,
1874, p. 321.
With respect to sexual differences
of colour, Dr. Gunther does not
know of any striking instance
either with frogs or toads; yet
he can often distinguish the
male from the female by the tints
of the former being a little
more intense. Nor does he know
of any striking difference in
external structure between the
sexes, excepting the prominences
which become developed during
the breeding-season on the front
legs of the male, by which he
is enabled to hold the female.*
It is surprising that these animals
have not acquired more strongly-marked
sexual characters; for though
cold-blooded their passions are
strong. Dr. Gunther informs me
that he has several times found
an unfortunate female toad dead
and smothered from having been
so closely embraced by three
or four males. Frogs have been
observed by Professor Hoffman
in Giessen fighting all day long
during the breeding-season, and
with so much violence that one
had its body ripped open.
* The male alone of the Bufo
sikimmensis (Dr. Anderson, Proc.
Zoolog. Soc., 1871, p. 204) has
two plate-like callosities on
the thorax and certain rugosities
on the fingers, which perhaps
subserve the same end as the
above-mentioned prominences.
Frogs and toads
offer one interesting sexual
difference, namely, in
the musical powers possessed
by the males; but to speak of
music, when applied to the discordant
and overwhelming sounds emitted
by male bullfrogs and some other
species, seems, according to
our taste, a singularly inappropriate
expression. Nevertheless, certain
frogs sing in a decidedly pleasing
manner. Near Rio Janeiro I used
often to sit in the evening to
listen to a number of little
Hylae, perched on blades of grass
close to the water, which sent
forth sweet chirping notes in
harmony. The various sounds are
emitted chiefly by the males
during the breeding-season, as
in the case of the croaking of
our common frog.* In accordance
with this fact the vocal organs
of the males are more highly-developed
than those of the females. In
some genera the males alone are
provided with sacs which open
into the larynx.*(2) For instance,
in the edible frog (Rana esculenta) "the
sacs are peculiar to the males,
and become, when filled with
air in the act of croaking, large
globular bladders, standing out
one on each side of the head,
near the corners of the mouth." The
croak of the male is thus rendered
exceedingly powerful; whilst
that of the female is only a
slight groaning noise.*(3) In
the several genera of the family
the vocal organs differ considerably
in structure, and their development
in all cases may be attributed
to sexual selection.
* Bell, History British Reptiles,
1849, p. 93.
*(2) J. Bishop, in Todd's Cyclopaedia
of Anatomy and Physiology, vol.
iv., p. 1503.
*(3) Bell, ibid., pp. 112-114.
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.*
With the huge tortoise of the
Galapagos Islands (Testudo nigra)
the males are said to grow to
a larger size than the females:
during the pairing-season, and
at no other time, the male utters
a hoarse bellowing noise, which
can be heard at the distance
of more than a hundred yards;
the female, on the other hand,
never uses her voice.*(2)
* Mr. C. J. Maynard, the American
Naturalist, Dec., 1869, p. 555.
*(2) See my Journal of Researches
during the Voyage of the Beagle,
1845, p. 384.
With the Testudo
elegans of India, it is said "that the combats
of the males may be heard at
some distance, from the noise
they produce in butting against
each other."*
* Dr. Gunther, Reptiles of British
India, 1864, p. 7.
CROCODILIA.-
The sexes apparently do not
differ in colour; nor
do I know that the males fight
together, though this is probable,
for some kinds make a prodigious
display before the females. Bartram*
describes the male alligator
as striving to win the female
by splashing and roaring in the
midst of a lagoon, "swollen to
an extent ready to burst, with
its head and tail lifted up,
he springs or twirls round on
the surface of the water, like
an Indian chief rehearsing his
feats of war." During the season
of love, a musky odour is emitted
by the sub-maxiliary glands of
the crocodile, and pervades their
haunts.*(2)
* Travels through
Carolina, &c.,
1791, p. 128.
*(2) Owen, Anatomy of Vertebrates,
vol. i., 1866, p. 615.
OPHIDIA.- Dr.
Gunther informs me that the
males are always
smaller than the females, and
generally have longer and slenderer
tails; but he knows of no other
difference in external structure.
In regard to colour, be can almost
always distinguish the male from
the female, by his more strongly-pronounced
tints; thus the black zigzag
band on the back of the male
English viper is more distinctly
defined than in the female. The
difference is much plainer in
the rattle-snakes of N. America,
the male of which, as the keeper
in the Zoological Gardens shewed
me, can at once be distinguished
from the female by having more
lurid yellow about its whole
body. In S. Africa the Bucephalus
capensis presents an analogous
difference, for the female "is
never so fully variegated with
yellow on the sides as the male."*
The male of the Indian Dipsas
cynodon, on the other hand, is
blackish-brown, with the belly
partly black, whilst the female
is reddish or yellowish-olive,
with the belly either uniform
yellowish or marbled with black.
In the Tragops dispar of the
same country the male is bright
green, and the female bronze-coloured.*(2)
No doubt the colours of some
snakes are protective, as shewn
by the green tints of tree-snakes,
and the various mottled shades
of the species which live in
sandy places; but it is doubtful
whether the colours of many kinds,
for instance of the common English
snake and viper, serve to conceal
them; and this is still more
doubtful with the many foreign
species which are coloured with
extreme elegance. The colours
of certain species are very different
in the adult and young states.*(3)
* Sir Andrew Smith, Zoology
of S. Africa: Reptilia, 1849,
pl. x.
*(2) Dr. A.
Gunther, "Reptiles
of British India," Ray Soc.,
1864, pp. 304, 308.
*(3) Dr. Stoliczka, Journal
of Asiatic Society of Bengal.,
vol. xxxix, 1870, pp. 205, 211.
During the breeding-season
the anal scentglands of snakes
are
in active function;* and so it
is with the same glands in lizards,
and as we have seen with the
submaxiliary glands of crocodiles.
As the males of most animals
search for the females, these
odoriferous glands probably serve
to excite or charm the female,
rather than to guide her to the
spot where the male may be found.
Male snakes, though appearing
so sluggish, are amorous; for
many have been observed crowding
round the same female, and even
round her dead body. They are
not known to fight together from
rivalry. Their intellectual powers
are higher than might have been
anticipated. In the Zoological
Gardens they soon learn not to
strike at the iron bar with which
their cages are cleaned; and
Dr. Keen of Philadelphia informs
me that some snakes which he
kept learned after four or five
times to avoid a noose, with
which they were at first easily
caught. An excellent observer
in Ceylon, Mr. E. Layard, saw*(2)
a cobra thrust its head through
a narrow hole and swallow a toad. "With
this encumbrance be could not
withdraw himself; finding this,
he reluctantly disgorged the
precious morsel, which began
to move off; this was too much
for snake philosophy to bear,
and the toad was again seized,
and again was the snake, after
violent efforts to escape, compelled
to part with its prey. This time,
however, a lesson had been learnt,
and the toad was seized by one
leg, withdrawn, and then swallowed
in triumph."
* Owen, Anatomy of Vertebrates,
vol. i., 1866, p. 615.
*(2) "Rambles in Ceylon," in
Annals and Magazine of Natural
History, 2nd series, vol. ix.,
1852, p. 333.
The keeper in the Zoological
Gardens is positive that certain
snakes, for instance Crotalus
and Python, distinguish him from
all other persons. Cobras kept
together in the same cage apparently
feel some attachment towards
each other.*
* Dr. Gunther, Reptiles of British
India, 1864, p. 340.
It does not,
however, follow because snakes
have some reasoning
power, strong passions and mutual
affection, that they should likewise
be endowed with sufficient taste
to admire brilliant colours in
their partners, so as to lead
to the adornment of the species
through sexual selection. Nevertheless,
it is difficult to account in
any other manner for the extreme
beauty of certain species; for
instance, of the coral-snakes
of S. America, which are of a
rich red with black and yellow
transverse bands. I well remember
how much surprise I felt at the
beauty of the first coral-snake
which I saw gliding across a
path in Brazil. Snakes coloured
in this peculiar manner, as Mr.
Wallace states on the authority
of Dr. Gunther,* are found nowhere
else in the world except in S.
America, and here no less than
four genera occur. One of these,
Elaps, is venomous; a second
and widely-distinct genus is
doubtfully venomous, and the
two others are quite harmless.
The species belonging to these
distinct genera inhabit the same
districts, and are so like each
other that no one "but a naturalist
would distinguish the harmless
from the poisonous kinds." Hence,
as Mr. Wallace believes, the
innocuous kinds have probably
acquired their colours as a protection,
on the principle of imitation;
for they would naturally be thought
dangerous by their enemies. The
cause, however, of the bright
colours of the venomous Elaps
remains to be explained, and
this may perhaps be sexual selection.
* Westminster Review, July 1,
1867, p. 32.
Snakes produce
other sounds besides hissing.
The deadly Echis
carinata has on its sides some
oblique rows of scales of a peculiar
structure with serrated edges;
and when this snake is excited
these scales are rubbed against
each other, which produces "a
curious prolonged, almost hissing
sound."* With respect to the
rattling of the rattle-snake,
we have at last some definite
information: for Professor Aughey
states,*(2) that on two occasions,
being himself unseen, he watched
from a little distance a rattle-snake
coiled up with head erect, which
continued to rattle at short
intervals for half an hour: and
at last he saw another snake
approach, and when they met they
paired. Hence be is satisfied
that one of the uses of the rattle
is to bring the sexes together.
Unfortunately he did not ascertain
whether it was the male or the
female which remained stationary
and called for the other. But
it by no means follows from the
above fact that the rattle may
not be of use to snakes in other
ways, as a warning to animals
which would otherwise attack
them. Nor can I quite disbelieve
the several accounts which have
appeared of their thus paralysing
their prey with fear. Some other
snakes also make a distinct noise
by rapidly vibrating their tails
against the surrounding stalks
of plants; and I have myself
heard this in the case of a Trigonocephalus
in S. America.
* Dr. Anderson, Proc. Zoolog.
Soc., 1871, p. 196.
*(2) The American Naturalist,
1873, p. 85.
LACERTILIA.-
The males of some, probably
of many kinds of lizards,
fight together from rivalry.
Thus the arboreal Anolis cristatellus
of S. America is extremely pugnacious: "During
the spring and early part of
the summer, two adult males rarely
meet without a contest. On first
seeing one another, they nod
their heads up and down three
or four times, and at the same
time expanding the frill or pouch
beneath the throat; their eyes
glisten with rage, and after
waving their tails from side
to side for a few seconds, as
if to gather energy, they dart
at each other furiously, rolling
over and over, and holding firmly
with their teeth. The conflict
generally ends in one of the
combatants losing his tail, which
is often devoured by the victor." The
male of this species is considerably
larger than the female;* and
this, as far as Dr. Gunther has
been able to ascertain, is the
general rule with lizards of
all kinds. The male alone of
the Cyrtodactylus rubidus of
the Andaman Islands possesses
pre-anal pores; and these pores,
judging from analogy, probably
serve to emit an odour.*(2)
* Mr. N. L. Austen kept these
animals alive for a considerable
time; see Land and Water, July,
1867, P. 9.
*(2) Stoliczka, Journal of the
Asiatic Society of Bengal, vol.
xxxiv., 1870, p. 166.
The sexes often
differ greatly in various external
characters.
The male of the above-mentioned
Anolis is furnished with a crest
which runs along the back and
tail, and can be erected at pleasure;
but of this crest the female
does not exhibit a trace. In
the Indian Cophotis ceylanica,
the female has a dorsal crest,
though much less developed than
in the male; and so it is, as
Dr. Gunther informs me, with
the females of many iguanas,
chameleons, and other lizards.
In some species, however, the
crest is equally developed in
both sexes, as in the Iguana
tuberculata. In the genus Sitana,
the males alone are furnished
with a large throat pouch (see
fig. 33), which can be folded
up like a fan, and is coloured
blue, black, and red; but these
splendid colours are exhibited
only during the pairing-season.
The female does not possess even
a rudiment of this appendage.
In the Anolis cristatellus, according
to Mr. Austen, the throat pouch,
which is bright red marbled with
yellow, is present in the female,
though in a rudimental condition.
Again, in certain other lizards,
both sexes are equally well provided
with throat pouches. Here we
see with species belonging to
the same group, as in so many
previous cases, the same character
either confined to the males,
or more largely developed in
them than in the females, or
again equally developed in both
sexes. The little lizards of
the genus Draco, which glide
through the air on their rib-supported
parachutes, and which in the
beauty of their colours baffle
description, are furnished with
skinny appendages to the throat "like
the wattles of gallinaceous birds." These
become erected when the animal
is excited. They occur in both
sexes, but are best developed
when the male arrives at maturity,
at which age the middle appendage
is sometimes twice as long as
the head. Most of the species
likewise have a low crest running
along the neck; and this is much
more developed in the full-grown
males than in the females or
young males.*
* All the foregoing
statements and quotations,
in regard to
Cophotis, Sitana and Draco, as
well as the following facts in
regard to Ceratophora and Chamaeleon,
are from Dr. Gunther himself,
or from his magnificent work
on the "Reptiles of British India," Ray
Soc., 1864, pp. 122, 130, 135.
A Chinese species
is said to live in pairs during
the spring; "and
if one is caught, the other falls
from the tree to the ground,
and allows itself to be captured
with impunity"- I presume from
despair.*
* Mr. Swinhoe, Proc. Zoolog.
Soc., 1870, p. 240.
There are other and much more
remarkable differences between
the sexes of certain lizards.
The male of Ceratophora aspera
bears on the extremity of his
snout an appendage half as long
as the head. It is cylindrical,
covered with scales, flexible,
and apparently capable of 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 (see C. stoddartii,
fig. 34) the whole appendage
is converted into a horn, which
is usually of a white colour,
but assumes a purplish tint when
the animal is excited. In the
adult male of this latter species
the horn is half an inch in length,
but it is of quite minute size
in the female and in the young.
These appendages, as Dr. Gunther
has remarked to me, may be compared
with the combs of gallinaceous
birds, and apparently serve as
ornaments.
In the genus Chamaeleon we come
to the acme of difference between
the sexes. The upper part of
the skull of the male C. bifurcus
(see fig. 35), an inhabitant
of Madagascar, is produced into
two great, solid, bony projections,
covered with scales like the
rest of the head; and of this
wonderful modification of structure
the female exhibits only a rudiment.
Again, in Chamaeleo owenii (see
fig. 36), from the west coast
of Africa, the male bears on
his snout and forehead three
curious horns, of which the female
has not a trace. These horns
consist of an excrescence of
bone covered with a smooth sheath,
forming part of the general integuments
of the body, so that they are
identical in structure with those
of a bull, goat, or other sheath-horned
ruminant. Although the three
horns differ so much in appearance
from the two great prolongations
of the skull in C. bifurcus,
we can hardly doubt that they
serve the same general purpose
in the economy of these two animals.
The first conjecture, which will
occur to every one, is that they
are used by the males for fighting
together; and as these animals
are very quarrelsome,* this is
probably a correct view. Mr.
T. W. Wood also informs me that
he once watched two individuals
of C. pumilus fighting violently
on the branch of a tree; they
flung their heads about and tried
to bite each other; they then
rested for a time and afterwards
continued their battle.
* Dr. Buchholz, Monatsbericht
K. Preuss. Akad., Jan., 1874,
p. 78.
With many lizards
the sexes differ slightly in
colour, the
tints and stripes of the males
being brighter and more distinctly
defined than in the females.
This, for instance, is the case
with the above Cophotis and with
the Acanthodactylus capensis
of S. Africa. In a Cordylus of
the latter country, the male
is either much redder or greener
than the female. In the Indian
Calotes nigrilabris there is
a still greater difference; the
lips also of the male are black,
whilst those of the female are
green. In our common little viviparous
lizard (Zootoca vivipara) "the
under side of the body and base
of the tail in the male are bright
orange, spotted with black; in
the female these parts are pale-greyish-green
without spots."* We have seen
that the males alone of Sitana
possess a throat-pouch; and this
is splendidly tinted with blue,
black, and red. In the Proctotretus
tenuis of Chile the male alone
is marked with spots of blue,
green, and coppery-red.*(2) In
many cases the males retain the
same colours throughout the year,
but in others they become much
brighter during the breeding-season;
I may give as an additional instance
the Calotes maria, which at this
season has a bright red head,
the rest of the body being green.*(3)
* Bell, History of British Reptiles,
2nd ed., 1849, p. 40.
*(2) For Proctotretus, see Zoology
of the Voyage of the Beagle;
Reptiles by Mr. Bell, p. 8. For
the lizards of S. Africa, see
Zoology of S. Africa: Reptiles,
by Sir Andrew Smith, pls. 25
and 39. For the Indian Calotes,
see Reptiles of British India,
by Dr. Gunther, p. 143.
*(3) Gunther in Proceedings,
Zoological Society, 1870, p.
778, with a coloured figure.
Both sexes of many species are
beautifully coloured exactly
alike; and there is no reason
to suppose that such colours
are protective. No doubt with
the bright green kinds which
live in the midst of vegetation,
this colour serves to conceal
them; and in N. Patagonia I saw
a lizard (Proctotretus multimaculatus)
which, when frightened, flattened
its body, closed its eyes, and
then from its mottled tints was
hardly distinguishable from the
surrounding sand. But the bright
colours with which so many lizards
are ornamented, as well as their
various curious appendages, were
probably acquired by the males
as an attraction, and then transmitted
either to their male offspring,
or to both sexes. Sexual selection,
indeed, seems to have played
almost as important a part with
reptiles as with birds; and the
less conspicuous colours of the
females in comparison with the
males cannot be accounted for,
as Mr. Wallace believes to be
the case with birds, by the greater
exposure of the females to danger
during incubation. |