Darwin's Theory of Sexual Selection 193 
In regard to those species of fish in which both sexes are 
equally ornamented, Darwin returns once more to his hy- 
pothesis that the color of the male, acquired through sexual 
selection, may be transmitted to the other sex, and then, as 
if in doubt on this point, he adds, that it may be the result 
of the “nature of the tissues and of the surrounding condi- 
tions.” He even makes the suggestion, somewhat further 
on, that the colors may be warning, although it is confess- 
edly unknown that these fish are distasteful to fish-devouring 
animals. 
In amphibians the crest on the back of the male triton, 
which becomes colored along its edge, is described as a second- 
ary sexual character. The vocal sacs, present in some species 
of frogs, are found sometimes in both sexes, but more highly 
developed in the males. In other species, as in the toad, it 
is the male alone that sings. In the reptiles we find that the 
two sexes of the turtles are colored alike, and this holds also 
for the crocodiles. Some male turtles make sounds at the 
breeding season, and the same is true for the crocodiles, the 
males of which are said to make a “prodigous display.” In 
snakes the males are smaller, as a rule, than the females, and 
the colors are more strongly pronounced, and although some 
snakes are very brilliantly colored, Darwin puts this down 
either to protective coloration, or to mimicry of other kinds 
of snakes. But surely the extremely brilliant colors of many 
snakes cannot be accounted for in any of these ways. The 
cause of the color of the venomous kinds, that are supposed 
to be imitated by the others, ‘remains to be explained and 
this may perhaps be sexual selection.” 
“Tt 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 colors in their partners, so as to lead to the 
adornment of the species through sexual selection. Never- 
theless, it is difficult to account in any other manner for the 
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