46 SEXUAL ORGANS. 



with a firm capsule. These egg-capsules, in their various shapes, 

 will be described in the discussion of the development of the 

 animals. 



Male Organs. These are simpler than those of the female 

 (pi. 3, fig. 18, 20) : the efferent canal is not divided into so many 

 succeeding portions, but instead a copulatory organ (penis) is 

 placed anteriorly, the structural peculiarities of which present 

 much that is noteworthy. 



The sperm gland or testicle lies embedded in the liver in the 

 same way as the ovarium usually, 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, flocky looking, whitish mass, which 

 like the ovarium presents an acinose structure. The efferent 

 ducts of the simple lobes and lobules then collect together on 

 the right side of the body into the vas deferens. 



The single testicular lobnles 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 de- 

 velopment 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. 



A penis is wanting in the Trochoidea and Scutibranchiates of 

 ( uvier, and the male sexual opening is here placed just as in the 

 female, immediately behind and to the left of the anus. The 

 penis is an outgrowth from the body wall, and is not evertible and 

 retractile in the prosobranchiates as in the pulmonates, though 

 having at times a cavity within. It is a fleshy, often very long 



