Organs in certain Puhnogasteropoda. 93 
muscular parietes,, and^ after passing for a short distance 
through the parietes of the body, terminates in the penis. 
The penis consists of an external bag, which forms a sort of 
prepuce, which contains a solid rod-like prolongation of the 
vas deferens ; this body, which recalls by its situation the glans 
penis, is grooved on one side and attached to the prepuce by 
the other, and terminates by two projecting lips; at the base 
of the groove is the opening of the vas deferens, surrounded 
by a projecting margin; the prepuce is attached to the walls 
of the body by two retractor muscles, and opens externally 
just behind the left tentacle. 
Eig. 2. — In LimncEUs stagnalis the dichogamic gland, con- 
trary to what takes place in P. corneus, is imbedded in that 
lobe of the liver which occupies the first whorl of the shell ; 
the caeca are globular, and are arranged on the excretory 
duct like a bunch of grapes. The ova and sperm-cells occupy 
the same position towards each other as in P. corneus ; the 
ova are of the same yellowish colour, and it would be impos- 
sible to distinguish the sperm- cells of L. stagnalis from those 
of P. corneus; the course of development is the same in 
both species ; the duct has the same kind of enlargement in 
its course as that of P. corneus, but it is not so large nor are 
the caeca upon it so long, it also tapers more gradually to its 
termination in the oviduct. The aibumeniparous gland lies 
close to the gizzard, and is directed transversely across the 
body. The oviduct is more easily separated from the vas 
deferens in this species than in F. corneus ; attached to it are 
two separate giand-like bodies, whose structure very much 
resembles that of the thickened part of the oviduct of P. 
corneus, and whose functions appear to be the same. Just be- 
fore the oviduct terminates in front of the opening to the 
lung it receives the duct of the spermatheca, which in this 
species is a globular sac. 
The vas deferens, on quitting the oviduct, has partly mus- 
cular and partly glandular walls, the muscular fibres forming 
a reticulum, between the meshes of which are situated minute 
gland-cells; the duct speedily becomes enlarged into a 
pyriform sac, after which it loses its glandular character, and 
becomes wholly muscular. I presume that the glandular 
walls and pyriform sac secrete a fluid analogous to that 
secreted by the prostate in the P. corneus, as the Limnseus 
possesses no distinct organ that answers to that gland ; the 
vas deferens, after becoming muscular, passes through the 
parietes of the body for a short distance, and terminates in 
the penis ; this is shaped like the italic letter s. The vas 
deferens opens into its posterior extremity on a small papilla, 
