SPECIAL ANATOMY. 233 



in length in different species of these gasteropods. The 

 head assumes two principal forms ; it is either sigmoid 

 and pointed, as in H. alholabns, H. multilineata, etc., or 

 else it is spiral and pointed, as in H. alternata, H. soli- 

 taria, etc. In the vas deferens, the spermatozoa may 

 often be detected in movement, which is slow and vibrat- 

 ing in character. 



The prostate gland, although situated along the tract 

 of the oviduct, evidently belongs to the male apparatus, 

 as is proved by its emptying solely into the vas deferens 

 in Vaginulus, and in its being placed between the ter- 

 mination of the epididymis and the commencement of 

 the vas deferens only, as is very conspicuously observed 

 in Succinea. In structure, it is composed of closely 

 packed, tortuous, tubular, simple folHcles, lined with 

 short, thick, pyramidal epitheha, Avhich are densely gra- 

 nular, and contain a round, nucleolated nucleus. The 

 object of this organ probably is to dilute the very tena- 

 cious spermatic matter as it oozes from the epididymis 

 into the spermatic groove on the inner side of the ovi- 

 duct. 



In all the terrestrial gasteropods examined, there was 

 found a small, glandular body, from which proceeds a 

 short duct to join the termination of the epididymis. It 

 consists of from two to nine rounded follicles joining a 

 common duct, and, from the constancy of its existence, 

 must be deemed important. 



The ovary is soft and homogeneous in appearance ; 

 viewed by the microscope, it is found to be almost wholly 

 VOL. I. 29 



