plain-coloured and unornamented. Lastly, in some few anomalous cases,
the females are more beautiful than the males. We shall often find, in
the same group of birds, every gradation from no difference between the
sexes, to an extreme difference. We shall see that female birds, like
female insects, often possess more or less plain traces or rudiments of
characters which properly belong to the males and are of use only to
them. The analogy, indeed, in all these respects between birds and
insects is curiously close. Whatever explanation applies to the one
class probably applies to the other; and this explanation, as we shall
hereafter attempt to shew in further detail, is sexual selection.
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
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