SiQ THE DESCENT OF MAN 



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 protection. 

 Conspicuous colors are likewise beneficial to manj;^ animals 

 as a warning to their would-be devourers that they are dis- 

 tasteful, or that they possess some special means of defence; 

 but this subject will be discussed more conveniently 

 hereafter. 



We can, in our ignorance of most of the lowest animals, 

 only say that their bright tints result either from the 

 chemical nature or the minute structure of their tissues, 

 independently of any benefit thus derived. Hardly any 

 color is finer than that of arterial blood; but there is no 

 reason to suppose that the color of the blood is in itself 

 any advantage; and, though it adds to the beauty of the 

 maiden's cheek, no one will pretend that it has been ac- 

 quired for this purpose. So again with many animals, 

 especially the lower ones, the bile is richly colored; thus, 

 as I am informed by Mr. Hancock, the extreme beauty of 

 the Eolidse (naked sea-slugs) is chiefly due to the biliary 

 glands being seen through the translucent integuments — this 

 beauty being probably of no sBrvice to these animals. The 

 tints of the decaying leaves in an American forest are de- 

 scribed by every one as gorgeous; yet no one supposes that 

 these tints are of the least advantage to the trees. Bearing 

 in mind how many substances closely analogous to natural 

 organic compounds have been recently formed by chemists, 

 and which exhibit the most splendid colors, it would have 

 been a strange fact if substances similarly colored had not 

 often originated, independently of any useful end thus 

 gained, in the complex laboratory of living organisms. 



The Suh-hingdom of the MoUusca. — Throughout this great 

 division of the animal kingdom, as far as I can discover, 

 secondary sexual characters, such as we are here consider- 

 ing, never occur. Nor could they be expected in the three 

 ' "Archives de Zoolog Bxp^r.," Oct. 1872, p. 563. 



