60 



(2) The blood supply of the gonad (from the posterior 

 artery) is identical with that of tlie gonad of other 

 primitive Gastropods, in which that organ distinctly 

 belongs to the post-torsional right side. Possibly, how- 

 ever, the other member of the ancestral pre-torsional pair 

 of gonads has fused with it. 



(3) The sex products are expelled into the right kidney, 

 and, perhaps, the extension of this organ on the ventral 

 surface of the hump is, in part, an attempt to preserve 

 its ancient connection with the gonad, an attempt which, 

 as we have seen, is partially unsuccessful. 



It is, however, not impossible that the apparently single 

 gonad has arisen from the fusion of the primitively 

 distinct pair. 



Development. 



(See figs. 35 to 42). 



The ovum has already been described as a small 

 globular body covered by a tough coat, which is incom- 

 plete at one spot — the micropyle. The sex products are 

 extruded into the surrounding sea water and fertilization 

 occurs in a haphazard fashion, the speinis entering via 

 the micropyle. Sperms seem to make their way 

 occasionally into the females, as ciliated embryos are 

 occasionally found which have not yet been extruded. It 

 is not impossible that hermaphroditism, to a very small 

 extent, may be rather more common than is supposed, 

 and this kind of variation would seem to be advantageous 

 to the animal, though self-fertilization has its draw- 

 backs. Fertilization may be obtained artificially by 

 injecting the sex products of one kind into the nuchal 

 cavity of a mature member of the other sex, or by 

 mixing both kinds of sex products in a small volume of 

 sea water. By observation of artificially fertilized ova, 



