148 



MAN, THE ANIMAL 



Figure 48. The entire central nervous S3'stem of one of the 

 shrimps (Branchipus venales), magnified ten times. Redrawn 

 from Hilton. There is a tendency toward a slight concentra- 

 tion of nervous tissue at the anterior end which is called the 

 brain. In applying the term brain to this nervous mass, there 

 is no thought of suggesting that it is similar to the brain shown 

 in Figure 49. 



Figure 49. The central nervous system and many of the 

 nerves of the seventeen-year locust. The nerve ganglia have 

 migrated toward the anterior end of the animal's body until 

 the posterior half contains nerves only. These two illustra- 

 tions show in a striking fashion the concentration of nervous 

 tissue into a brain. 



