80 EARTHWOKMS, LEECHES, AND SEAWORMS 



Its walls are thick, muscular; and capable of contractioD 

 and expansion. Following the pharynx is the slender, 

 thin-walled gullet which extends through eight segments 

 to the crop, a short reservoir formed by a dilatation of the 

 alimentary canal. Adjoining the crop is the gizzard, a 

 firm, muscular organ lined with a chitinous membrane. 

 The remaining part of the canal answers both as a stomach 

 and intestine. It is a straight, thin-walled tube without 

 glandular appendages such as the hver and pancreas found 

 in the higher animals (Fig. 41). 



The process of digestion. — Digestion begins before the 

 food even enters the mouth of the worm. A certain di- 

 gestive fluid is poured forth from the mouth to moisten the 

 food about to be eaten. It is thought that Hme secretions 

 from certain glands connected with the gullet mix with the 

 food while passing through this organ and neutraUze the 

 acids produced by the leaves. The gizzard grinds the food 

 and is usually aided in this work by fine sand. The main 

 action of digestion goes on in the anterior part of the 

 stomach-intestine. 



The circulation of the earthworm. — This animal possesses 

 two circulations, the ccelomic circulation and the vascular 

 circulation, each being quite distinct from the other. The 

 coelome is fiUed with a colorless fluid which is driven to all 

 parts of the body by contractions of the body walls. This 

 fluid passes from one segment to another through holes in 

 the thin cross-partitions. It is supposed that the nutritive 

 portions of the food pass through the walls of the intestine 

 into the ccelomic fluid and are thus carried directly to all 

 the organs which this fluid bathes. 



The blood, or vascular circulation is fairly well developed, 

 for the blood is red and circulates through a system of 



