SEXUAL ORGANS. lit 



The sperm-gland or testicle lies imbedded in the liver in the 

 same wa}- as the oA^arium visually, only on the right side, as a 

 flocky mass which has a greater tendency to embrace the liver 

 than to crowd it away. Sometimes, however, it is a compact 

 mass, and in Paludina it is divided into but two lobes, a larger 

 anterior and a smaller posterior one. But in most cases the 

 testicle is a much expanded and divided, tlocky -looking, whitish 

 mass, which like the ovarium presents an acinose structure. 

 The elTerent ducts of the simple lobes and lobules then collect 

 together on the right side of the body into the vas deferens. 



The single testicular lobules consist of a structureless tunica 

 propria and an internal epithelium of rounded cells, in which the 

 zoosperms are developed. In all cases where the mode of devel- 

 opment can be followed, the contents of the epithelial cells 

 divide into daughter-cells, in which, after the development and 

 growth of a nucleus and the disappearance of the cell-wall, the 

 spermatozoa are developed. The zoosperms are filiform and 

 pointed at both ends in the spiral prosobranchs, but in Patella, 

 Chiton and Haliotis the anterior end is a rounded head. 



The vas deferens passes from the testicle along the columellar 

 side of the animal into the mantle-cavity, and through the latter 

 into the penis on the right side of the body, behind the eyes. 

 This duct is formed externally by a strong muscular layer, and 

 clothed within with a ciliated epithelium : it is usually dilated 

 and coiled at its commencement. 



In Paludina a part of the penis is lodged in the teguments of 

 the right, tentacle, which in consequence is sensibly deformed 

 and shorter and more obtuse than the right tentacle of the 

 female. In an Indian species of Paludina the penis is altogether 

 aborted and its function transferred to the contiguous right 

 tentacle, the extremity of which is hooked ; which becomes a 

 copulatory organ, analogous to the hectocotylized arm of the 

 cephalopods (Wood-Mason, Ann. Mag. Nat. Hist., viii, 87, 1881). 



The penis is an outgrowth from the body-wall, and is not 

 evertible and retractile in the prosobranchiates as in the pulmo- 

 nates, though having at times a cavity within. It is a fleshy, 

 often very long and thick appendage usually bent in a sigmoid 

 form, and can be bent back under the mantle and thus be hidden. 



The penis is either hollow, in which case the vas deferens pro- 

 ceeds to it as a closed canal passing through it to its extremitj^, 

 where it opens upon a small papilla as in Buccinum, or it opens 

 simply as in Littorina, Oliva, Oncidiopsis ; or, in other cases it 

 is a solid body upon which the vas deferens passes along in the 

 form of a ciliated furrow continued upon it as a deep groove to 

 its extremit}^, as in Triton, Dolium, Cassis, Harpa, Yoluta, 

 Terebra, Strombus, C.yprsea, etc. This last and most common 

 form of penis presents many varieties ; in Cassis, for example, it 



