136 BIOLOGICAL LECTURES. 



bryos there are fourteen pairs of segments and an anterior 

 unsegmented tip that may represent a single pair or several 

 consolidated pairs. This is a larger number of neural seg- 

 ments than has heretofore been counted for vertebrate animals. 

 It approaches more nearly the number of head myotomes as 

 determined by Dohrn and Killian. 



Finally, we are to conclude from a study of the neural seg- 

 ments that the vertebrate brain is primitively segmented to 

 its anterior tip ; that its segments do not, at first, differ from 

 those of the trunk, — in other words, they are homodynamous 

 with those of the spinal cord, — and that there are in sharks 

 fourteen pairs of segments. 



Whitman has shown by a masterly analysis of the brain and 

 nervous system of clepsine that the entire nervous system of 

 annelids may be regarded as a series of brains, and that, nor- 

 mally, a pair of these nerve-centers, or brains, belongs to each 

 segment. This, taken in connection with the facts set forth in 

 this lecture, enables us to look upon the human brain, not as a 

 homogeneous mass of tissue, but as a complex, composed of an 

 aggregation of about fourteen invertebrate brains, all united 

 into a working whole. We are to understand that its complex- 

 ity has been brought about through ages of responses to ex- 

 ternal and internal influences, and its perfection of physiological 

 action has been gradually attained. It is the highest product of 

 evolution, the goal towards which, in the morphological world, 

 nature has been working for countless aeons of time. 



