2l8 



COLLEGE ZOOLOGY 



General Internal Anatomy. — If a specimen is cut open from 



the anterior to the pos- 

 terior end by an in- 

 cision passing through 

 the body- wall a trifle 

 to one side of the mid- 

 dorsal line, a general 

 view of the internal 

 structures may be 

 obtained (Fig. 154). 

 As in Ascaris (p. 169, 

 Fig. 112 b), the body 

 is essentially a double 

 tube (Fig. 153), the 

 body-wall constitut- 

 ing the outer, the 

 straight alimentary 

 canal, the inner ; be- 

 tween the two is a cav- 

 ity, the ccelom (coel). 

 The external seg- 

 mentation corresponds 

 to an internal division 

 of the ccelomic cavity 

 into compartments by 

 means of partitions, 

 called septa (Fig. 154), 

 which lie beneath the 

 grooves. These septa 

 are absent in Ascaris. 

 The alimentary canal 

 passes- th *he 



center of t. 

 is suspended in - 

 ccelom by the parti- 



