309] NORTH AMERICAN POLYSTOMIDAE—STUNKARD 29 



ings. From these reservoirs, a wide vaginal txibe on either side runs 

 backwards and inwards, to open into the anterior lateral yolk duet." 

 A similar condition is described and figured by Zeller for P. integerri- 

 mum. In all other species in which the structure has been described, the 

 vaginae are open funnels leading mediad and dorsad from their openings 

 on the ventro-lateral surface of the body, and uniting just below the in- 

 testine with the common vitelline ducts to form the vitello- vaginal canals. 

 The cuticular lining of the vaginae is very thick and in the parenchyma 

 around the vaginae there are large cells of secretory type (Fig. 24). The 

 vitello-vaginal canals lead medially and unite, either forming a duet 

 which discharges into the ootype (Fig. 32) or opening separately into 

 the ootype (Figs. 3, 16, 24). 



From the ovary the oviduct passes posteriad and ventrad, opening 

 into the ootype. Immediately anterior and dorsal to the opening of the 

 oviduct, there branches from the ootype a small tube which after a some- 

 what twisted double loop opens into the intestine of the side in which the 

 ovary is situated. This genito-intestinal canal has been the source of 

 much controversy and its presence or absence is the diagnostic feature of 

 Odhner's two groups of monogenetic trematodes. Mehlis' gland, the shell 

 gland of earlier authors, is never largely developed and is difficult to 

 find in some specimens where it is represented by a few nuclei in the 

 parenchyma around the ootype. Zeller for P. integerrimum and John- 

 ston for P. iulliense described prominent "shell glands", and Stewart 

 for P. kachugae described ' ' a group of glandular cells found at the same 

 transverse level as the ovary, but on the opposite side of the midline. 

 They appear to be connected with the corresponding vagina, but their 

 function is obscure." Since they are in the precise location of the 

 Mehlis' gland, one is led to suspect that Stewart was confused in regard 

 to the connections and relations of this group of ceUs, altho in in- 

 dividuals of other species studied by the writer, there are groups of 

 large glandular cells in the parenchyma surrounding each vagina. 



The ootype is continued by a tube which passes anteriad on the op- 

 posite side from the ovary, and which leads to the uterus. Previous 

 writers have called this tube the oviduct and Johnston (1912) says, 

 "From the ootype, the oviduct runs forward to a point in front of the 

 ovary, whence it bends sharply backwards and runs in a straight course 

 close to the ventral surface, almost to the level of the cotylophore, where 

 it opens into the wide uterus. ' ' The use of the term oviduct for the tube 

 leading from the ootype to the uterus is confusing and objectionable. 

 Looss (1899) says, "Der Theil des weibMchen Leitungswegen, der den 

 Keimstock mit dem ootjrp verbindet, ist der oviduct oder Keimgang," 

 and this terminology is found in general use thruout the literature. In a 

 large number of trematode genera the ootype opens directly into the 



