ANATOMY OF POLYSTOMATIDAE 



the mucus in which the body is bathed, or to the attempts of the 

 host to free itself from these parasites ; and hence an investing 

 membrane is present, which morphologically is either a modified 

 epithelium, or a cuticle formed by the glandular secretion of the 

 parenchyma. 



The reproductive organs of the Polystomatidae may be under- 

 stood from Figs. 24, 27, and 28. At the point of union of the ovi- 



Fio. 24. Polystomum integer- 

 rimnm Frbh., from the 

 bladder of the Frog, aud 

 seen from the ventral sur- 

 face. The alimentary 

 canal is black, the white 

 dots upon it being the 

 yolk-glands, dvi, Ductus 

 vitello - intestinalis (pro- 

 bably homologous with 

 the Laurer's canal or 

 " vagina " of Digenea) ; 

 eh, hooks of sucking 

 disc; int, intestine; m, 

 mouth ; ov, ovary ; pe, 

 penis ; ph, pharynx ; sc, 

 suckers with an embryonic 

 hook persisting in each ; 

 te, testes ; ut, uterus with 

 eggs ; vag, left vagina ; 

 vd, vas deferens ; yd, 

 yolk - duct ; yg, yolk- 

 glands ; <J 9, common 

 genital aperture. (Modi- 

 fied fromZeller.) x 8. 



duct (Fig. 28, ovd}, the vitelline ducts (i/d),and the commencement 

 of the uterus (ut\ a slender duct is given off which opens into the 

 intestine, and is known as the " vitello-intestinal canal " (Fig. 24, 

 dvi ; Fig. 28, gic). This duct has apparently the same relations 

 as the " canal of Laurer " of Digenea, 1 except only that the latter 

 opens to the exterior directly. In connexion with this vitello- 

 intestinal canal a " vagina " is present, which in Polystomum and 

 most Monogenea is paired (Fig. 24, vag}, in Diplozoon and in one 

 1 See Leuckart, " Parasiten," Bd. ii. p. 238. 



