218 



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 A scar is (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 t 4 he 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 through the 

 center of the body, and 

 is suspended in the 

 ccelom by the parti- 



