VII. Round Worms 



Nematoidea. The central nervous system of nematode worms 

 was early described as a whole by Biitschli who recognized a collar 

 of nerve cells and fibers and longitudinal strands. Hesse, 1892, 

 gives a clearer picture of the nervous system of Asccdis and others 

 since that time have improved and elaborated upon these and other 

 early suggestions. Especially noteworthy are the works of Gold- 

 .schmidt, 1908-9, and Deineka, 1908, each very valuable although 

 the two investigators disagree on many points. 



The nervous system of Ascaris may furnish a good starting 

 point in a discussion of the nervous system of the group. In this 

 genus there is a circumoral ring about the pharynx near the anter- 

 ior end of the body. Ganglion cells are not abundant. They are 

 chiefly grouped about the origin of the nerves. The nerve ring gives 

 off six or more longitudinal nerves of which the mid-dorsal and mid- 

 ventral are usually the largest and are connected to each other by 

 fine branches. At the caudal end the lateral nerves pass into two 

 branches formed by the division of the ventral nerve. Just above 

 this point the ventral nerve swells into the anal ganglion. In the 

 male the anal ganglion gives oflT two lateral nerves which form a 

 ring about the cloaca. 



The nerve ring forms a plexus according to Goldschmidt, in 

 that all fibers are connected to other parts, but the plexus is regular 

 and not of the diffuse type as found in Coelenterata. Three cell 

 types are found, sensory, association and motor. Besides the direct 

 connection of cell with cell through their processes there is in places 

 a true neuropile. Neuroglia cells are found but are not prominent. 

 Deineka favors the neropile method of interrelation more than Gold- 

 schmidt. This author also has demonsti'ated the neurofibrillar 

 arrangement of the material with the nerve cells and has shown 

 rather elaborate interrelations between the fibrils of associated 

 cells. He shows nerve terminations in muscle and sensory endings 

 in the skin of the body. Aside from the general surface of the body 

 the three papillae about the mouth are the only sense organs. These 

 are supplied by six short nerves running from the nerve ring. 



With free living nematodes but little has been done. In Enoplas 

 Hilton, 1920, a very marked head ganglion above the mouth has two 

 strands running backwards to the thick mid-ventral nerve strand 

 and from the dorsal side a slender dorsal nerve runs the length of 

 the body. The ganglion is rather complex in structure. From an 

 inner group of nerve cells, fibers run forward to the sensory epithe- 

 lium of the tip of the snout and three eyes, one dorsal and two 

 ventro-lateral are composed of pigment and clear area in front. 



Magrath, 1919, in Callanus, gives a good account of the nervous 

 system of this simple nematode.- In this as in other forms, there is 



