SHALLOW-WATER FAUNA. 



47 



colours has led some naturalists to the belief that 

 they are of no importance to the species in the 

 struggle for existence, that they are, as it were, 

 the accidental result of some process of excretion, 

 and not the outcome of a long series of slight 

 changes, bringing about at length an adaptation 



FIG. 14. Smooth-shelled Gastropod. FIG 15. Spiny Gastropod. 



of form most suitable to the habits of the animal. 

 Such views are, however, to be accepted with 

 great caution, and most zoologists will be con- 

 tented to wait until our knowledge is much 

 greater than it is at present, before wholly agree- 

 ing with them, 



