390 THE DESCENT OF MAN. 



any fish, at least any fresh-water fish, is rejected from 

 being distasteful to fish-devouring animals. On the whoks 

 the most probable view in regard to the fishes, of which 

 both sexes are brilliantly colored, is that their colors were 

 acquired by the males as a sexual ornament, and were 

 transferred equally, or nearly so, to the other sex. 



We have now to consider whether, when the male differs 

 in a marked manner from the female in color 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 inconspicu- 

 ous for the sake of protection, such modifications being 

 inherited only by the females. It is impossible to doubt 

 that color 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 colors in adapta- 

 tion to surrounding objects, and that within a short time.* 

 One of the most striking instances ever recorded of an 

 animal being protected by its color (as far as it can be 

 judged of in preserved specimens), as well as by its form, 

 is that given by Dr. Giintherf of a pipe-fish, which, with 

 its reddish streaming filaments, is hardly distinguishable 

 from the sea-weed to which its 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 

 colored. The ova are fertilized immediately after being 

 deposited; and when this process lasts for several days, as 

 in the case of the salmon, J the female during the whole 



*G. Pouchet, L'lnstitut, Nov. 1, 1871, p. 134. 



t " Proc. Zoolog. Soc.," 1865, p. 327, pi. xiv and xv. 



j Yarrell, " British Fishes," vol. ii, p. 11. 



