152 



MANUAL OF ZOOLOGY 



canal, the pharynx or 



— *han 



-din 



Fig. 83. — Diagram of nervous 

 system of Nematoda. c, com- 

 missures; din, dorsal nerve; 

 /is;/, posterior lateral nerve; 

 on, upper and tin, under 

 portion of nerve-ring; sg, 

 lateral swellings ; vln, ventral 

 nerve. (From Lang, after 

 Biitschli.) 



stomodagum (Fig. 82, //;), with very 

 muscular walls. Posteriorly the 

 pharynx opens into the intestine 

 (in/), a thin walled tube, flattened 

 from above downwards. Posteriorly 

 the intestine narrows considerably 

 to form the short rectum, which 

 opens externally by the anus (an). 

 The food, consisting of the semi- 

 fluid contents of the intestine of the 

 host, is sucked in by movements of 

 the pharynx, and is then absorbed 

 into the system through the walls 

 of the intestine. The food being 

 already digested by the host, there 

 is no need of digestive gland-cells 

 such as occur in animals which pre- 

 pare their own food for absorption. 



Between the enteric canal and 

 the body-wall is a distinct space, the 

 ccelome or body-cavity, containing a 

 clear fluid. 



The excretory system presents a 

 certain resemblance to that of Pla- 

 todes. It consists of two longitu- 

 dinal canals (ex. v), one in ea'ch 

 lateral line. Anteriorly they pass 

 to the ventral surface, unite with 

 one another, and open by the 

 minute excretory pore (ex. p) al- 

 ready noticed. 



The nervous system consists of a 

 ring (nv. r) surrounding the pharynx 



