EARTHWORM 



349 



a larger, thin- walled structure, which extends through segment XVI. 

 This is followed by the muscular gizzard in segments XVII and 

 XVIII. A thin-walled intestine extends to the anus, which opens to 

 the outside through the last segment. 



The intestine is not a simple tube but has a large fold, the typhlo- 

 sole, protruding into its lumen from the dorsal side giving it more 

 absorptive surface for the assimilation of food. The coelomic side 

 of the intestine is covered with a layer of brown cells, known as 

 cliloragogen cells, whose function is doubtful. They are generally be- 

 lieved, however, to play a part in the excretion of nitrogenous wastes. 



dv 



n^ 



Fig. 128. — Cross section of an earthworm through a posterior segment, ch, 

 chloragogue cells ; cir, circular muscle fibers ; coe, coelom ; cu, cuticle ; dv, dorsal 

 blood vessel ; ep, epidermis ; int, intestine ; la, lateral neural vessel ; Id, parietal 

 vessel ; Ion, longitudinal muscle fibers ; n, nephridium ; nc, nerve cord ; sb, subneural 

 blood vessel; se, seta; Ty, typhlosole ; vv, vejitral blood vessel. (From White, Gen- 

 eral Biology, The C. V. Mosby Company.) 



The food of the earthworm consists of almost any kind of organic 

 matter which may pass through its digestive tract. The animals 

 remain in the soil during the daytime and work their way through 

 it by passing it continually through the digestive tract. At night 

 they come to the surface of the ground, usually remaining partly 

 within or very near the burrow, and feed on dead organic matter, 

 such as leaves. Food is drawn into the mouth by suction produced 



