122 SEXUAL ORGANS. 



extremity of the uterus — which adheres very slightly to the first 

 portion of the deferent canal, so that a slight traction suffices to 

 separate them ; consequently their walls are complete. 



We find in the course of the uterus a yellowish pocket having 

 glandular walls, in front of which the uterus swells, constituting 

 the egg-reservoir. This dilatation contracts to form the vagina, 

 in which opens the neck of the copulatory sac. The female 

 orifice opens at the base of the neck near the pulmonary opening. 



The deferent canal, in its adherent portion, is first flattened, 

 then dilates and becomes pyriform. Its anterior portion is 

 narrow cylindrical, and gains the base of the verge after having 

 traversed a muscular mass in which it appears to lose itself. The 

 male genital orifice is placed behind the right tentacle. 



In Limnsea and Planorbis the inter-muscular course of the 

 anterior portion of the deferent canal is very short, but in 

 Yaginula it is very long. This canal is not always complete ; in 

 Oncidium, Oncidiella, Aplysia, etc., it is replaced by a simple 

 gutter placed below the body, on the right side of the foot, or at 

 the superior right side of the neck. 



As in the monotremata, we find also in the ditremata accessory 

 organs annexed to the reproductive system. The excretory 

 canal of the ovotestis develops large and numerous glands 

 (Ancylus) ; a seminal vesicle is inserted in the deferent canal 

 (Vaginula) ; one or several diverticular appendages open in the 

 vagina (Oncidiella, Melampus) ; very numerous mucous or 

 multifid vesicles open in the sack of the verge (Vaginula ) ; an 

 extremely long flagellum is inserted in the posterior extremity of 

 the penis-sack (Peronia), etc. 



T/iePieropoc^aai'e androgynous, their genital system resembling 

 that of the Opisthobranchiates or of the ditremate pulmonates. 

 In Hyalsea, there exists in eff'ect : a rather large hermaphrodite 

 gland, the excretory canal of which is provided with a 

 long epididymic caecum ; a matrix to the posterior part of 

 wtiich adheres a sort of albuminiparous gland ; a vagina where 

 the copulatory pouch opens. The female is separated from the 

 male orifice. The deferent canal is separate from the matrix 

 and gains the verge, the orifice of which is near the mouth. In 

 the ditremate pulmonata and the opisthobranchiates the copu- 

 latory act, of course, cannot be reciprocal between two individuals ; 

 one of them must take the part of female, the other of male ; but 

 a third can be male for the second, and so on, ad infinitum. 

 Such is the mode of copulation in Aplysia fasciata. Fischer 

 has seen chains formed by six individuals, the first functionally 

 as female only, the following ones as male with the preceding 

 and as female with the succeeding individual, the last fvilfilling 

 the role of male only, Geoff'roy has seen similar chains formed 

 hy the Limnseans. In Helix copulation is reciprocal, each indi- 



