84 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



S /- 



.o. 



regulates and guides the activity of the other 

 ganglia? 



In our analysis of the nerve-functions we will begin 

 with the earthworm. We will consider first its pro- 

 gressive movements, and will attempt to answer the 

 question, Does coordinated progressive movement, in 



which all the segments of 

 C. the body participate, de- 

 pend upon the brain (<?, 

 Figs. 27 and 28) ? The 

 locomotion of the earth- 

 worm is a very simple 

 process. The setse play 

 an important role, although 

 they are not visible to the 

 naked eye ; they act like 

 locomotor appendages and 

 give the animal a hold on 

 FIG. 27. DORSAL VIEW OF THE CEN- the ground. The real mus- 



TRAL NERVOUS SYSTEM OF AN des Q{ l ocomotion how . 

 EARTHWORM. 



ever, are contained in the 



0, supraoesophageal ganglion ; c, commissure ; 



, suboesophageal ganglion ;.?, pharynx ; CUtanCOUS ITlUSCle - layCT. 

 G, ganglia of the ventral cord. . . . 



1 his consists of ring-fibres 



and longitudinal fibres. When the worm begins to 

 move, the ring-fibres contract first, causing the worm 

 to become longer and thinner. The bristles are 

 turned backward and, because of the resistance of 

 the ground, prevent the animal from moving back- 

 ward. In this way the head is pushed forward. As 

 soon as the maximum elongation has been reached, 



