128 



ANIMAL COLORATION. 



discovered. Tritonia plebeia is, according to Prof. Herdman, 

 ■generally found creeping over the surface of colonies of 

 Alojonium digitatum — " Dead men's fingers " ; its colours, like 

 those of the polyp, are various shades of yellow, brown, 

 and grey. Dendronotus (see fig. 10) is marked with purple, 

 brown, and yellow tints, and it is to be met with among 

 masses of brown and yellow zoophytes. It is true that the 



Fig. 10. — Eolis and Dendronotus. 



similarity between these molluscs and their living environment 

 is heightened by the dorsal processes already referred to ; 

 these processes simulate the polyps in various degrees of ex- 

 pansion and retraction ; but this resemblance would not be of 

 much advantage, were the colours in striking contrast. That 

 the resemblance in coloration is due to the action of natural 

 selection, and not to the direct transference of pigment from 

 the polyps upon which the nudibranchs browse, cannot be for 



