234 COMPARATIVE ANATOMY CHAP. 



aperture. The male aperture and the penis lie in front of the female, far forward on 

 the head or neck ; the two apertures are quite distinct, and both lie on the right. 



This second type may be deduced from the first, if we assume not only that the 

 common duct of the hermaphrodite gland divided into a male and a female duct, 

 but also that the seminal furrow closed to form a canal in continuation of the 

 male duct. 



When the duct of this second type split into a male and a female duct, the 

 accessory organs also so divided that the male opened into the vas deferens, the 

 female into the oviduct. 



To this type belong, among the Pulmonata, the Basommatophora, a few species 

 of Daudcbardia (D. Saulcyi, in which the two apertures lie close together), the 

 Oncidia, and Vaginulidce. In both these latter groups, the female aperture has 

 followed that part of the pallial complex which shifted to the posterior end of the 

 body, and lies near the anus. The male aperture has, however, retained its anterior 

 position on the head, behind the right cephalic tentacle. The two apertures thus 

 lie at the opposite ends of the body. Among the Opisthobranchia, this second type 

 is exemplified in Oscinius (Tectibranchia). 



Taking Limnaea stagnalis and Oncidium as examples, we find in the former 

 (Fig. 191) that the hermaphrodite gland which lies embedded in the " liver," high 

 up in the visceral dome, gives rise to a thin hermaphrodite duct ; this soon divides 

 into a male and a female duct. The male duct first widens into a flattened sac, 

 then into a large pear-shaped glandular vesicle (prostata). From this vesicle it runs 

 as a long thin vas deferens through part of the pedal musculature, and finally enters ' 

 the male copulatory apparatus, which is, in fact, merely the widened muscular and 

 protrusible end of the vas deferens. A small penis tube is first formed by the vas 

 deferens, and this projects on a papilla into a subsequent larger tube (the penis 

 sheath), which is evaginated during copulation. Protractors are attached to the 

 sheath, and retractors to the small tube ; the latter alone with its papilla enters the 

 vulva during copulation. 



An albuminous gland opens into the female duct immediately after its separation 

 from the male duct. It then forms a uterus consisting of wavy folds, and is continued 

 into a large pear-shaped body as oviduct, the narrow end of which is the vagina and 

 leads to the female genital aperture. The oviduct receives a lateral accessory gland 

 called the nidamental gland, and the vagina the efferent duct of the globular 

 receptaculum seminis. 



In Oncidium celticum (Fig. 192) the hermaphrodite gland and female accessory 

 glands lie in the posterior part of the body, between the lobes of the liver and the 

 coils of the intestine. From the gland rises a hermaphrodite duct, which at one 

 point carries a small lateral csecum, and opens into an irregularly-shaped organ, the 

 uteltis. Within the uterus two projecting folds border a channel ; if these folds 

 become apposed, the channel becomes a tube. This channel runs from the point of 

 entrance of the hermaphrodite duct to the point where the seminal duct leaves the 

 uterus, and serves for conducting the semen. The remaining wider portion of the 

 uterus serves as oviduct and egg-reservoir, and carries a large caeca! appendage ; 

 the ducts of the two much-lobed albuminous glands also enter the uterus. 



A comparison of Limncea and Oncidium shows that in the latter the male and 

 female ducts separate from one another further back than in the former. The vas 

 deferens in Oncidium is only incompletely separated as a groove in the uterus. Its 

 differentiation into a separate duct takes place here, as in terrestrial Pulmonates, at 

 the distal end of the uterus. The thin seminal duct (vas deferens) passes into the 

 body wall to the right, and runs forward along the longitudinal furrow between the 

 foot and back, passing again at the anterior end of the body into the primary body 

 cavity, where it forms numerous coils, and finally enters the copulatory apparatus. 



