CHAPTER II 



NOTES ON THE ANATOMY OF THE FOOD 

 MOLLUSKS 



OME time before the publication of Darwin's 

 " Origin of Species " in 1859, a few natu- 

 ralists had come to believe that similarity in 

 structure in different species of animals or 

 plants could be explained only on the assumption that 

 these species were more closely related to each other than 

 to other species. To them it seemed unlikely that the 

 many points of resemblance in structure and habit to 

 be found in comparing scores of varieties or species 

 of violets, for example, could mean anything but a rela- 

 tionship between them. From the analogy afforded by 

 different breeds of domesticated animals, known to be 

 derived from a common parent form, it seemed reason- 

 able to assume that several kinds of thrushes, or of crows, 

 of squirrels, hares, or similar groups of species differing 

 only slightly from each other in nature, had descended 

 one from another or from common ancestors. 



But this view was then founded merely on analogy 

 and met with little favor. The world continued to hold 

 tenaciously to the still less reasonable hypothesis that each 

 species of animal and plant had originated independently 

 in an act of special creation. According to this tradi- 

 tional belief, no relationship existed between different 

 species. The Creator of the animate world had decided 



