48 Laboratory Guide in Zoology 



vessel around the alimentary canal to join the longi- 

 tudinal ventral blood-vessel. These aortic arches form 

 the centres of the blood system. 



VIII. — The most conspicuous bodies now exposed are the 

 white-lobed seminal vesicles in the tenth and eleventh 

 segments. They are connected by ducts with external 

 openings on the ventral surface of the iifteenth seg- 

 ment. 



IX. — The alimentary canal is composed of five parts, 

 named as follows, beginning at the anterior end : 

 pharynx, oesophagus, crop, gizzard, and intestine: Dis- 

 tinguish each. The pharynx is continuous with the 

 mouth and has light-colored muscular walls ; it extends 

 to about the seventh segment. The oesophagus is a 

 straight tube, generally extending from the eighth to 

 the sixteenth segments. Near the sixteenth segment 

 the alimentary canal is enlarged, forming a sort of thin- 

 walled pouch ; this is the crop. Directly back of it is 

 the muscular gizzard. The rest of the canal forms the 

 intestine. Make a drawing of the canal. 



X. — Over the pharynx, near the anterior end, find two 



small white oval bodies, which form the central part of 

 the nervous system : they are the cerebral ganglia. Re- 

 move the intestine carefully, and find a white ventral 

 nerve cord extending longitudinally. 



XL — The ventral blood-vessel will be found extending 

 longitudinally below the alimentary canal. It may be 

 necessary to use another specimen in order to demon- 

 strate it. 



XII. — Carefully push aside the ahmentary canal from 

 about the eighth to about the fourteenth segment. The 

 very small white bodies to be seen in the base of the 

 thirteenth segment are the ovaries. Near these are two 



