SEXUAL SELECTION. 295 



jelly-fish (Medusa, Porpita, etc.), some Planarise, many 

 star-fishes, Echini, Ascidians, etc.; but we may conclude 

 from the reasons already indicated, namely, the union of 

 the two sexes in some of these animals, the permanently 

 affixed condition of others, and the low mental powers of 

 all that such colors do not serve as a sexual attraction and 

 have not been acquired through sexual selection. ^ It 

 should be borne in mind that in no case have we sufficient 

 evidence that colors have been thus acquired, except where 

 one sex is much more brilliantly or conspicuously colored 

 than the other, and where there is no difference in habits 

 between the sexes sufficient to account for their different 

 colors. But the evidence is rendered as complete as it can 

 ever be only when the more ornamented individuals, almost 

 always the males, voluntarily display their attractions 

 before the other sex; for we cannot believe that such dis- 

 play is useless, and if it be advantageous sexual selection 

 will almost inevitably follow. We may, however, extend 

 this conculsion to both sexes when colored alike if their 

 colors are plainly analogous to those of one sex alone in 

 certain other species of the same group. 



How, then, are we to account for the beautiful or even 

 gorgeous colors of many animals in the lowest classes? It 

 appears doubtful whether such colors often serve as a pro- 

 tection; but that we may easily err on this head will b& 

 admitted by every one who reads Mr. Wallace's excellent 

 essay on this subject. It would not, for instance, at first 

 occur to any one that the transparency of the Medusae, or 

 jelly-fish, is of the highest service to them as a protection; 

 but when we are reminded by Hiickel that not only the 

 Medusae but many floating mollusca, crustaceans and even 

 small oceanic fishes partake of this same glass-like appear- 

 ance, often accompanied by prismatic colors, we can hardly 

 doubt that they thus escape the notice of pelagic birds and 

 other enemies. M. Giard is also convinced* that the 

 bright tints of certain sponges and ascidians serve as a pro- 

 tection. Conspicuous colors are likewise beneficial to many 

 animals as a warning to their would-be devourers that they 

 are distasteful, or that they possess some special means of 

 defense; but this subject will be discussed more conven- 

 iently hereafter. 



AVe can in our ignorance of most of the lowest animals 



* " Archives de Zoolog. Ex per. " Oct., 1872, p. 563. 



