HEEMAPHRODITISM IN MOLLUSCA. 23- 



number of genera by various authors (Hancock, Bergh, 

 Trinchese, and myself) ; the same is the case with those 

 Nudibranchs in which the male and female acini are easily 

 distinguished under a lens of low power (e. g. Fiona). 



It must be noticed, however, that in Eolis (Coryphella) 

 Landsburgii the acini of the hermaphrodite gland produce 

 ova in their distal portion and spermatozoa in their proximal 

 portion (8) ; this arrangement has been recognised as general 

 in all the Elysioidea (Cyerce, Hermsea, Elysia, Lima- 

 pontia). 



(8) Pulmonata. — In these Gasteropods the genital gland is 

 formed of hermaphrodite acini both in the Stylommatophora 

 (e.g. Helix) and in the Basommatophora (e.g. Auricula). 



In Siphonaria (Basommatophora), according to Haller 

 (9), each acinus of the hermaphrodite gland is exclusively of 

 one sex, either male or female. In S. Algesirae, which I 

 have studied, I have observed that the conformation of the 

 gland is precisely analogous to that found in Onchidiopsis, 

 the Pleurobranchidse, and the Nudibranchia, — that is to say, 

 the peripheral female acini open into the more centrally 

 situated male acini. 



However, this conformation is not so entirely different from 

 that presented by the other Pulmonata. I know cases, in fact, 

 in which the wall of the genital gland already shows a distinct 

 sexual differentiation upon the two sides of the follicles, and 

 in which the female side exhibits projections which are the 

 rudiments of acini of this sex (Araphibola). 



It follows, then, from what has been said above, that 

 examples of the various possible modes in which the genital 

 gland is constituted are to be found side by side in all the sub- 

 groups of hermaphrodite Gastropods. 



3. Lamellibranchia. 



(1) Ostrea. — The question of sex in oysters has long been 

 a subject of controversy, and its solution, which presents 

 decided difficulties, is not yet universally recognised. 



