ASCARIS 



137 



Lateral nerve 



Submedian 

 nerve. 



Sublateral 

 nerve . 



Ventral 

 nerve . 



Dorsal 

 nerve. 



body and have the power of taking up particles from the body 

 cavity. They are known from this function as the phagocytic 

 cells. The nerve cords 

 (Fig. 100) are connected 

 by transverse commis- 

 sures in the ectoderm, 

 and in front join a ring Lateral 

 a little way behind the ^^'^^^"^'^' 



mouth. From this ring ^^^^^^i 



four other cords run gangUon 

 back at the sides, and 

 six forward. The nerve 

 ring is slightly thickened 

 above and rather more 

 below, and contains 

 some nerve cells. The 

 only other ganglia are 

 placed at the sides of 

 the nerve ring and at 

 the hinder end of the 

 ventral cord. A few 

 cells are scattered 

 among the fibrils of 

 which the cords are 

 composed, but there is 

 no sign of segmental 

 arrangement in these or 

 any other organ of the 

 body. The number of 

 cells which compose the 

 nervous system is small 

 and remarkably con- 

 stant, each cell being 

 recognisable in the same 



position in every individual. Each muscle fibre (Fig. loi) consists 

 of an outer part which has fibrils running longitudinally and an 

 inner part of undifferentiated cytoplasm containing a nucleus. 

 Strands of protoplasm stretch from the inner parts of the muscle 

 fibres to the dorsal and ventral nerves. The alimentary canal con- 

 sists of three parts : a short stomodaeum, or fore-gut, known as 

 the pharynx, a long mid-gut, and a short proctodaeum, or hind-gut, 



Anal __ 

 ganglion 



Fig. 100. 



Anus 



A diagram of the nervous system of 

 a nematode. 



