•62 THE EARTHWOEM 



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. 



Gi(,t 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, and especially the five pairs of 

 ' hearts.' 



For the dissection of the circulatory system a fresh worm 

 should he tahen. Owing to the dark red colour of the con- 

 tained blood the vessels can be readily traced. The dissection 

 ■is best performed under spirit. 



1. The dorsal vessel is a large median vessel running along 

 the dorsal surface of the alimentary canal throughout 

 its whole length ; and dividing in front into branches 

 ramifying over the pharynx. It can be seen through 

 the skin in the living animal, and the flow of blood 

 in it is from behind forwards. 



A large lateral oesophageal vessel runs along 

 each side of the cesophagus, and communicates with 

 the dorsal vessel in the tenth segment. Branches of 

 it ramify over the pharynx and over the oesophageal 

 glands and pouches. 



From the alimentary canal the blood is returned 

 to the dorsal vessel by intestinal vessels, of which 

 there are in the region of the intestine two to each 

 segment. 



