GASTEROPODA. 



399 



Fig. 196. 



near the right tentacle, where it protrudes, as 

 in the Snail, for the purpose of copulation, 

 by the inversion of its walls ; it is, however, 

 absolutely imperforate, and receives no duct 

 by which it can communicate with the testis 

 so as to become instrumental in immission; 

 but externally a deep groove is seen upon its 

 surface when in a state of protrusion, which is 

 continuous with a long furrow seen upon the 

 surface of the body, continued from the base 

 of the penis to the orifice of the female ap- 

 paratus. Fig. 197 represents the secreting 



Fig. 197. 



portions of this system removed from the body, 

 and displayed so as to expose the internal 

 structure of the parts composing it. The 

 ovary (h) is a large oval, whitish, and granular 

 mass, from which the oviduct arises by several 

 distinct tubes which emerge from different 

 parts of its substance : this oviduct opens into 

 the common tube (e\ which may be called the 

 vagina. The mass (f,g\ called by Cuvier 

 the testis, and supposed by him to be solid 

 and homogeneous in its texture, is found, when 

 opened, to be divided by spiral septa, resem- 

 bling the scala cochleae in the ears of Mam- 

 malia (g), and thus forms a long spiral cavity 

 communicating with the commencement of the 

 vagina, in which latter tube we also find aper- 

 tures by which the vesicle (p) and the larger 

 sacculus (o) communicate with the common 

 passage. 



In Onchidium, an aquatic species belonging 

 to the inoperculate pulmonary order, the male 

 and female parts are in a similar manner 

 placed at opposite extremities of the body, 

 but the former assume a more complicated 

 structure than in the Tectibranchiata, which 

 we have described. The ovary (Jig. 198, A, a, a) 



Fig. 198. 



Generative organs of Aplysia. 



Generative organs of Onchidium, 



consists of two masses replete with ova, each 

 of which furnishes a short duct ; the two thus 

 formed unite into a convoluted tube (6), which 

 is the common oviduct : arriving at the mass 

 always regarded by Cuvier as the testis, it 

 enlarges and forms within the substance of 

 that organ many convolutions, on emerging 

 from which it runs directly in the shape of a 

 narrow canal (d), to the external orifice (h). 

 The bladder (f) receives a large duct (e) from 

 the mass here assumed to be the testis, and 

 gives off another of equal size, which joins the 

 oviduct (d) prior to its termination. This 



