254 



ZOOLOGY 



SECT. 



by some fluid derived from their host. Pigment occurs in some 

 of the ectoparasitic forms. 



cil 



FIG. '203. Monogenetic Trematodes. A, Gyrodactylus. cil. disc bearing hooks and pro- 

 cesses at the posterior end ; ent. intestine ; gl. unicellular glands whose ducts open on the 

 surface about the anterior end ; li\. caudal disc of the first embryo ; h. caudal disc of the 

 second embryo ; mo. mouth ; oosp. oosperm ; ov. ovary ; p. penis ; ph. pharynx ; te. testes. 

 B, Polystomum. en. intestine ; g. p. genital pore ; mo. mouth ; ph. pharynx ; or. ovary ; te. 

 testes ; it. uterus ; v., v. d. vas del'erens ; rit. vitt'lline glands ; rit. <l. vitelline ducts ; x 

 marks the position of the genito-intestinal canal connecting tin 1 oviduct with the intestine. 

 (From M. liratin.) 



The relationship of the Cestoda to the Trematoda is, as will be 

 subsequently shown, fairly close ; but though there are connecting 



