80 EARTIIWORMy, LEECHES, AND SEAW(JRMS 



Its walls ai'e thick, iiiii,^cular, ainl capable of coiitraetioD 

 and expansion. Following the phaiynx is the slender, 

 thin-\\"alk'il gullet wiiiiii extends through eight segments 

 to the crop, a .'-horl reservoir formed by a dilatation of the 

 alimentary cana.l. Adjoining the crop is the gizzard, a 

 hrm, muscular organ lined with a chitinous meml)rane. 

 The remaining |)art oi the canal answers both as a stomach 

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

 glandular ajiijcndages such as the liver and pancreas found 

 in the higher animals (Fig. 41). 



The process of digestion. — Digestion Ijegins before the 

 f(Hjd even enters the mouth of Ihe worm. A certain di- 

 gestive fluid is i)Oured forth iVoni the mouth to moisten the 

 food atiout to be eaten. It is tliought that lime secretions 

 fiom certain glands connected witli the gullet mix with the 

 food ^\iiile passing tJvroiigh lliis organ and neutralize the 

 acids produced l)y the leaves. The gizzard grinds the food 

 and is usually aided in this work l)y iine 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 cuiomic circulatinu and the vascular 

 circulation, eacli being (juite distinct from the other. The 

 cfclonie is filled with a t'olorless fluid which is driven to all 

 parts of the body by cimti'actions of the liody walls. This 

 fluid ]iasscs from one .scgmeid' to another through holes in 

 the thin ci'oss-|iai titions. It. is siijiposcd that the mitritive 

 poiiions of the fooil pass tlu-ough the walls of the intestine 

 into (he c(('lomic ihiid and a,re thus carried directly to all 

 the organs which this fluid bathes. 



The blood, orA'ii.sciikir (irculation is fairly well de^'eloped, 

 for the blood is led and circulates through a system of 



