CIRCULATORY SYSTEM 61 



4. The crop is a large dilatation of the alimentary canal 



in segments xm. to xvi., but when filled it encroaches 

 upon the segments in front, pushing the septa before 

 it (fig. 16). 



5. The gizzard extends from the sixteenth segment back- 



wards to about the twentieth. Its walls are very 

 thick and muscular, and it has a thick chitinous 

 lining. 



6. The intestine is a thin-walled sacculated tube running 



straight backwards from the gizzard to the anus. 



a, The * hepatic cells ' are a layer of yellow cells sur- 



rounding the intestine and in close relation with 

 the blood-vessels. Their function is unknown. 



Cut the intestine open along one side, and wash out its 

 contents. 



b, The typhlosole is a prominent median longitudinal 



ridge projecting into the cavity of the intestine 

 from its dorsal wall, of which it is a fold. Its 

 surface is marked by transverse folds. 



C. The Circulatory System. 



The blood is a fluid coloured bright red by haemoglobin 

 and containing colourless corpuscles. Several of the larger 

 vessels contract rhythmically, but there is not a distinct 

 heart. 



For the dissection of the circulatory system a freshly 

 killed worm should be taken, which has not been in spirit. 

 Owing to the dark red colour of the contained blood the 

 vessels can be readily traced. 



1. The dorsal or supra-intestinal vessel runs from the 



hinder end of the body forwards as far as the 

 pharynx, over which it ramifies, forming a plexus of 

 smaller vessels. 



2. Lateral vessels arise in pairs from the sides of the dor- 



sal vessel, and run round the sides of the alimentary 

 canal. Their arrangement differs in different parts 

 of the body. 



