SECTION V 



The Nervous System 



The nervous system of Apus does not at first sight 

 seem to support our theory as obviously as does the 

 musculature. This, however, is the case only at first 

 sight. A closer study of it, and a comparison of it 

 with that of an Annelid modified by having its five 

 anterior segments bent in the way assumed, leave but 

 little doubt concerning its origin. The central nervous 

 system of Apus can in fact be shown to be the central 

 nervous system of a bent Annelid adapted to the 

 necessities of a new manner of life ; the principal 

 modification being due to the migration of the eyes on 

 to the dorso-frontal surface. 



Figure 17 shows the general type of the nervous 

 system of a carnivorous Annelid, such as the ancestor 

 of Apus may be supposed to have possessed. The 

 longitudinal commissures may perhaps have been 

 somewhat wider apart. ^ We find the brain in the 



^ See however p. 80. 



F 2 



