2 68 Shell Life 



mass in a number of little points or long waving 

 plumes (cerata), which are often coloured by portions 

 of the creature's food or by the bile. These colours 

 appear in different instances to have the effect of 

 disofuising the mollusk or of warnino^ its enemies 

 that it is not good to eat. 



Until recently the remarkable forms and colours 

 of these creatures were not considered to have any 

 special significance, and it is particularly surprising 

 that even Darwin failed to note the relation of form 

 and habit here, so keen as he always was in such 

 cases. It is true that here he was seeing through 

 the eyes of others. Had he been addicted to the 

 study of marine zoology in his later years he would 

 probably have modified or rewritten certain para- 

 graphs in the Descent of Man : for example (p. 261) : — 



" We can in our ignorance of most of the lower 

 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. . . . So . . . with many animals, especially 

 the lower ones, the bile is richly coloured ; thus, as 

 I am informed by Mr. Hancock, the extreme beauty 

 of the Eolida3 (naked Sea-slugs) is chiefly due to the 

 biliary glands being seen through the translucent 

 integuments — this beauty being probably of no 

 service to these animals." And again (p. 264) : " That 

 many of the nudi branch mollusca, or sea-slugs, are as 

 beautifully coloured as any shells may be seen in 

 Messrs. Alder and Hancock's magnificent work ; and 

 from information kindly given me by Mr. Hancock, 

 it seems extremely doubtful whether these colours 

 usually serve as a protection. With some species 



