136 The Molluscan Family Planorhidae 



increases to double its diameter near the end where the vas deferens enters. 

 There is a single, wide retractor muscle (RM) which may be split into 

 several branches (figs. 1, 5). The duct of the penial gland (DC) is very 

 long and narrow (8 mm. to 9 mm. long) and extends from the upper part of 

 the preputium to a point just above the diaphragm (see fig. 8). Normally 

 the duct lies coiled on the preputium just over the jienial gland and ad- 

 herent to the preputium, bound down by many small muscles covering the 

 preputial sac. There is usually one wide band of sui)porting nuiscle (SM). 

 The duct is shown in fig. 5 partly uncoiled. 



Internally (fig. 8), the preputial cavity (PR) contains a number of 

 small vertical folds or pilasters. There is a large, cup-shaped penial gland 

 (GL) about 1 mm. in diameter, which is contracted near its attachment 

 to the body wall of the i)reputium to form a narrow, roundeil neck. The 

 duct (DGj passes through the wall of the j^reputium and extends to the 

 vergic sac where it enters just above the diaphragm (DV). A vertical sec- 

 tion of the gland (fig. 4j shows the circular cup to be of considerable depth 

 (about 1 mm.), the inner walls lined with many vertical folds (GF). The 

 bottom of the cup contains many small folds placed longitudinally. The 

 gland duct (DC) enters the bottom folds of the cup. The walls of the cu]) 

 (BW) are very thick. Another form of gland is shown in fig. 14. 



The vergic sac contains the elongated verge (V) which is enlarged at 

 the upper end and tajicrs downward to a point. The seminal canal has a 

 central exit beyond which a small, triangular papilla extends, as shown in 

 fig. 10. There is a large muscular ring or diaphragm (1)1 which is capable 

 of considerable extension and contraction, causing the diaphragm to be a 

 narrow nmscular ring or a comjiarativcly thin membrane which nearly 

 closes the opening between the preputium and vergic sac. Figure 10, some- 

 what diagranunatic, shows the relationship between the diaphragm, the 

 verge, and the entrance of the penial ghmd (hict. which is a trifle too high 

 in the figure. 



The penial complex often assumes a bilobatc lorm, the preputium ex- 

 tending ujnvard until it is higher than the vergic sac (fig. Ij. A vertical 

 section of such a condition (fig. 2) shows the penial gland to be placed at 

 the sununit of the preputial extension. The relationshi]) of the verge and 

 the penial gland duct is also shown in this section. In young specimens of 

 three and one-half whorls, the prei)utium and vergic sac form a single wide, 

 elongate-pyriform i)enial complex with a short penial gland duct (fig. 3). 

 This condition is suggestive of typical Helisoma, which has a wide penial 

 complex and a short duct, and indicates, it would seem, a develoi)ment of 

 the Pierosoma group from the HeUso))ia group. 



Female Organs (fig. 15) . The spermatheca fS) is elongate-pyriform 

 and about 2 nun. long. The si)ermathecal duct (SD) is 3 mm. long, narrow, 

 and somewhat enlarged at the lower end where it enters the short and 

 wide vagina (YG). The uterus (U) is about 7 mm. long, narrow at the 

 vagina and widening to double this diameter near the prostate where it 

 unites with the nidamental gland (NG), which is wide and bulbous. The 

 oviduct (OD) is short and wide (about 3.5 mm. long and 0.5 nun. wide) 

 and somewhat coiled. The albumen gland (fig. 7) is sciuarish and is com- 

 posed of many small follicles. In side view, it is seen to be cleft to accom- 

 modate the passage of the intestine on its lower surface (fig. 6, IN). There 

 is a large carrefour (fig. 15, CF) into which the duct of the albumen gland 

 enters (DA). 



