SPECIAL ANATOMY. 233 
in length in different species of these gasteropoda. The 
head assumes two principal forms ; it is either sigmoid 
and pointed, as in H. albolabris, 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 Yaginulus, 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 follicles, lined with 
short, tbick, pyramidal epitbelia, which are densely gra- 
nular, and contain a round, nucleolated nucleus. Tbe 
object of tbis 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. 60 
