254 



ZOOLOGY 



SECT. 



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

 of the ectoparasitic forms. 



FIG. 203. JYlonogenetic 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 ; hi. caudal disc of the first embryo ; fa. 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 ; ov. ovary ; te. 

 testes ; u. uterus ; y., v. d. vas deferens ; vit. vitelline glands ; vit. d. vitelline ducts ; x 

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

 (From M. Braun.) 



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

 subsequently shown, fairly close ; but though there are connecting 



