PTEROPODA AND OASTUOPODA. 



563 



The modifications of the parts of the complex combined organs of 

 the androgynous Gastropods are manifold. In regard to their ulti- 

 mate terminations or outlets, a common genital orifice is found in 

 J)oris, Tritonia, Thetis, Biilimus, Clausilin, and Limax, as in the 

 above described Helix. In Planorbis and Physa the male and female 

 orifices are situated side by side ; the male in front, on the left side 

 of the neck, behind the tentacle. In Bulla, Bullcea, and Aplysia, 

 the male orifice is under the right tentacle, the female one much 

 further back. In Doridium the male orifice is beneath the left ten- 

 tacle ; the female one on the same side, but near the opposite end of 

 the body. In Onchidium the female orifice is situated close to the 

 anus at the posterior end of the body ; the male orifice is beneath the 

 right tentacle. In all cases where the male and female organs are 

 separate, a furrow may be traced from one to the other : the penis, 

 when everted, projects from the male orifice. 



The dioecious Gastropods form two sections, in one of which the 

 copulatory organs are wanting, in the other highly developed. The 

 non-copulants include the Cyclobranchiata and Scutibranchiata ; 

 the other section comprises the operculated Pulmonata, the Hetero- 

 poda, and the Pectinibranchiata. In these the intromittent organ is 

 usually of extraordinary length : it is grooved in most, perforated in 

 a few ; capable of retraction in the Paludina, but doubled back upon 

 the outside of the mantle when drawn into the shell by the Buccinum 

 and Strombus. In the Carinaria it is bifid. 



The internal organs of the male whelk, represented in the annexed 

 figure, consist simply of a testis 

 and sperm-duct. The testis (a) is 

 of considerable size, sharing with 

 the liver the smaller convolutions 

 of the shell ; from this arises the 

 vas deferens, which forms by its 

 convolutions a kind of epididymis 

 {b), and then increasing in dia- 

 meter enters the root of the penis, ■ 

 through which it passes by a tor- 

 tuous course (</) to the tubercle at 

 the extremity of this organ, where 

 it opens externally. The penis is 

 composed of strong transverse fas- 

 ciculi of muscle, with lacunar sinu- 

 ses, which together cause the erec- 

 tion of this organ : the muscles will at the same time lengthen it, and 



o o 2 



Male organs of Buccinum. 



