32 STUDIES OF ANIMAL LIFE. 



d. Beginning at the anterior end identify the fol- 

 lowing modifications of the alimentary canal, — 



(1) the pharynx, a whitish muscular enlarge- 



ment of the canal extending to the seventh 

 somite ; 



(2) the oesophagus, a thin-walled tube extending 



to the twelfth somite; (It is usually 

 partly covered by the thickened septa of 

 this region.) 



(3) the crop, an abrupt enlargement of the canal ; 



(4) the gizzard, a thick-walled enlargement; 



(The crop and gizzard occupy about 

 three somites.) 



(5) the stomach-intestine, the remainder of the 



alimentary canal. 



5. The Nerve Cord. 



The nerve cord is a white thread-like structure 

 lying imder the alimentary canal. 



a. What is its extent ? 



b. How does it end anteriorly ? Look for the 



" brains " on the dorsal anterior surface of the 

 pharynx. 



c. Observe the ganglia, slight enlargements of the 



nerve cord. There is one in each somite. 



d. Observe very small lateral branches of the nerve 



cord in each somite. (Dem.) 



6. The Circulatory System. 



a. Identify in the body cavity the two blood-vessels 

 (dorsal vessel and ventral vessel) which you saw 

 in the living worm. 



I. Observe six pairs of large lateral vessels 

 ("hearts") connecting the dorsal and ventral 

 vessels in the region of the oesophagus. 



