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TEXTBOOK OF ZOOLOGY 



calciferous glands, the secretions of whicli help to neutralize the acid 

 organic matter taken as food. The esophagus opens into the crop, 

 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 



•<lv 



Fig. 105. — Cross section of the earthworm through a posterior segment, ch, 

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

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

 branch of dorsal vessel ; loti, longitudinal muscle fibers ; n, nephridium ; nc, nerve 

 cord ; sb, subneural blood vessel ; se seta, ty, typhlosole ; vv, ventral blood vessel. 

 (Prom White, General Biology.) 



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

 chioragogen cells, whose function is doubtful. They are generally 

 believed, however, to play a part in the excretion of nitrogenous 

 wastes. 



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 



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