The Origin of the Brain 67 



system and sensory organs which enabled them 

 to meet the demands of the conditions to which 

 they were exposed. 



The class of beings (Vermes) which include 

 the various orders of worms follow the star-fish 

 in the natural ascending classes of animals ; of 

 these we may refer to the common earth-worm 

 to illustrate the link which exists between the 

 structural development of a central nervous 

 system, and the growth of instinctive processes. 

 It is probable that earth-worms have been 

 developed from fresh-water, and these from 

 marine, ancestors. 1 When these animals came 

 to dwell on the land they must have begun to 

 move with one part of their bodies in front, and 

 thus acquired an anterior end or head, and sides 

 to their bodies. The head of the organism 

 being thus brought into constant contact with 

 external objects, its sensitive elements, includ- 

 ing nerve cells connected with its skin layer, 

 were developed by use, and at the same time 

 became protected by passing from the surface 

 deeper into the head ; in this way an aggrega- 



1 Comparative Anatomy of Animals, by Gilbert C. Bourne, 

 Vol. II., p. 4?, 



E 2 



