ROUND WORMS 



57 



a cephalic commissure. With this are associated twenty nerve cells 

 on each lateral half and a large number just anterior to it. From 

 these last groups six slender nerves pass forward close to the oeso- 

 phagus to supply the anterior region. The two sub-ventral have 

 small ganglia upon them. Connected with the caudal edge of the 

 nerve ring are four chief ganglia, one dorsal, one ventral and two 

 lateral. Each of these has long strands extending tow-ards the tail 



Fig. 16. The figure above is a reconsti'uction of the head end of Enophis, 

 showing the position of the nei'vous system. The lower figure at the 

 left is of a section through the whole body of the worm, showing the 

 dorsal and ventral nerve bands. Both these figures enlarged 75 

 times. The drawing at the right is from a section through the head 

 ganglion, enlarged 170 times. The dorsal side is up in all the figures. 

 Hilton. 



end of the animal. Continued from the ventral and separated a 

 little distance is another ventral ganglion, the post- ventral. The 

 dorsal cephalic ganglion is the smallest; the lateral cephalic ganglia 

 are the largest. As pointed out by others the cephalic commissure 

 or nerve ring is essentially fibrous. The fibers are derived from the 

 ganglia connected with it. 



