VII 



MOLLUSGA—GENITAL ORGANS 



231 



Loligo (B), however, the funnel-shaped depression into which all the testicular 

 canals open is replaced by a longitudinal furrow, into wliich these converging canals 

 open. In Sepia (C), the germinal body has no ligament, but lies immediately in 

 front of the anterior wall of the gonad, and is thus outside the genital cavity. The 

 germinal body here has a central channel towards which the radially arranged 

 seminal canals converge from all sides, and which they enter. This channel, again, 

 opens through an efferent duct into the genital cavity, from which the spermatozoa 

 are conducted to the exterior by the seminal duct. 



The spermatozoa of the Mollusca are of the common pin shape. In many species 

 of Prosobranchia two different forms of spermatozoa, the liair-shaped and the vermi- 

 form, occur in one and the same individual. This phenomenon has by some been 

 taken as an indication of developing hermaphroditism, and by others as pointing to 

 a fonner hermaphrodite condition ; in the first case tlie vermiform spermatozoa 

 would be the eggs beginning to form, in the second the rudiments of eggs. There 

 is, however, no solid foundation for eitlier of these views. 



With regard to the question whether the hermaphrodite or the dioecious condition 

 is the original condition, the latter alternative may be considered as the more prob- 

 able. Of the five classes of the Mollusca, two, the Scaphopoda and the Cephalopoda, 



Fio. 189.—^, B, C, Three diagrams of tlie male gonads of, the Cephalopoda. A, ordinary- 

 type. B, Loligo. C, Sepia. 1, Seminal duct ; 2, cavity of the gonad ; 3, space into which all the 

 canals of the testis open, and which itself opens into the cavity of the gonad, in Sepia, by means 

 of a canal (4) ; 5, suspensor of the male germinal body, attaching it to the^anterior wall of the 

 gonad. 



are altogether dioecious. Among tlie Amphineura, the Ohitonidce, which most 

 recent observers hold to be less specialised than the Sole7wgastres, are sexually 

 separate. Among the Lamellihranchia, the sexes are separate in the Protobranchia, 

 which are rightly considered as primitive forms ; and most other bivalves are also 

 dioecious. Among the Gastropoda, the sexes are separate in the Prosobranchia, 

 especially in the Diotocardia, which are universally considered to be the lowest and 

 least specialised Gastropods. 



b. The ducts. — The manner in which the sexual products are conducted to the 

 exterior in the Amphineura, Scaphopoda, and Lanullibranchia need not again be 

 discussed, as it has already been described in the general part of this section, and in 

 the section on the nephridial system. We thus have now only to treat of the very 

 complicated ducts of the Gastropoda and the Cephalopoda. 



(1) Gastropoda. — It has been seen that in all Diotocardia (Haliotis, Fissurella, 

 Patella, etc.) the genital products are ejected through the right kidney. In 

 the Monotocardia, the right kidney has atrophied as such, but, according to the 

 most recent investigations, its duct persists as genital duct. In the Pulmonata 

 and Opistlwbranchia, the genital aperture is no longer in the mantle cavity. 



