344 The Descent of Man. Part II. 



We have now to consider whether, when the male differs in a 

 marked manner from the female in colour or in other orna- 

 ments, 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 "Sshes 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. 22 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. Giinther 33 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 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 



32 G. Povchet, L'JWitut No*. 1, 327, pi. xiv. and xv. 

 1871, p. 134. « Yarrell, ' British Fishes,' vol 



w 'Pvoe. Zoolog. Soc." A 8fiS, p. ii. p. 11. 



