Chap. XII. 
FISHES. 
19 
evidence on this head. 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 sex ; 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 
of smaller size, 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 
most conspicuously coloured. The ova are fertilised 
immediately after being deposited, and when this pro- 
cess lasts for several daj^s, as in the case of the salmon,"^ 
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 pre- 
served, and both would have an equal influence on the 
colours of their offspring or the race. 
Certain fishes, belonging to several families, make 
nests ; and some of these fishes take care of their 
young when hatched. Both sexes of the brightly- 
coloured Crenilahrus massa and melons w^ork together in 
building their nests with sea-weed, shells, &c.^^ But the 
males of certain fishes do all the work, and afterwards 
take exclusive charge of the young. This is the case 
Yarrell, ‘ British Fishes/ vol. ii. p. 11. 
According to the observations of M. Gerbe; see Giinther’s ‘Ee- 
cord of Zoolog. Literature/ 1865, p. 194. 
c 2 
