152 



MANUAL OF ZOOLOGY 



-din 



canal, the pharynx or stomodaeum (Fig. 82, pk), with very 

 muscular walls. Posteriorly the 

 pharynx opens into the intestine 

 (int), 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 each 

 lateral line. Anteriorly they pass 

 to the ventral surface, unite with 



Fig. 83. — Diagram of nervous one another, and open by the 



system of Nematoda. c, com- . / \ i 



missives; din, dorsal nerve; minute excretory pore (ex. p) al- 



hsn, posterior lateral nerve; . . 



on, upper and mi, under reaGy noticed. 



portion of nerve-ring; sir, n-M j • ±. r 



lateral swellings ; vin, ventral T-he nervous system consists of a 

 Bu t v S chiiS From Lang ' af ' er ring (nv. r) surrounding the pharynx 



> 



-han 



