II. TREMATODA: DISTOME.E 



245 



Order II. Distomeae (Digenea). 

 The entoparasitic Trematodes usually occur as sexual animals in the 

 digestive tract and its appendages; more rarely in blood-vessels, urogenital 



^S^'cf^-siy^'N.. 



Fig. 220. — Development of Distomum hepaticum (from Korschelt-Heider after 

 Leuckart). .4, young larva; B, sporocyst from the lung of Limnaa; C, older sporocyst 

 with rediie; D, redia which has produced redise internally; E, redia with cercarise; F, 

 cercaria; G, encysted Distomum. A, eye spot; D, digestive tract; Dr, glands; Ex, 

 ciliated lobules and main trunks of excretory system; G, birth opening; Kz, germ cells; 

 N, nervous system. 



organs, and ccelom of vertebrates. As inhabitants of the dark they have, 

 with few exceptions, lost the eyes, which appear in larval life, and not 

 always then. Since not exposed to danger of being pulled from the host, 



