3G0 REPRODUCTIVE ORGANS — SPERM DUCT AND VAS DEFERENS. 
first part of the ovispermatoduct which may he hollowed for its 
reception and with which it comninnicates. It varies in size, not 
only according to the species but periodically, being very voluminous 
at the pairing season, when it plentifully secretes a viscid albuminous 
fluid containing globules and granular matter with which the descend- 
ing ova become surrounded. 
The Sperm Duct (a-kpiLa, seed) in the dioecious species originates at 
the testis or male gonad, it is often of considerable length and may 
follow a tortuous course, usually becoming differentiated as a pros- 
tatic glandular enlargement in some part of 
its course before reaching the male organ. 
In the monoecious species there is a 
combined conduit or hermaphrodite duct 
which conveys both ova and sperm, the two 
becoming separated at the seminal vesicle, 
the ova following the oviduct, and receiv- 
ing their store of albumen, etc., and the 
zoosperms passing down the conjoint sperm 
duct which is attached to the concave side 
of the oviduct and beset with glandular follicles, forming a prostate, 
which becomes greatly swollen at pairing times ; the separation between 
the oviduct and sperm duct may be incomplete, as in Avion, in which 
the two channels communicate along their whole combined course. 
The Vas Deferens {vas, a vessel; defero, to carry away) is the 
sperm conduit when freed from adherence to the oviduct and before 
its arrival at the male organ ; on its course it may develop a seminal 
sac, as in Limnau, or become enlarged near its termination, and 
secrete the si)ermatophore, as in Hyalinia. In 
some of the primitive Exophalliate Gastropods 
the .sperm duct terminates externally in the 
pallial region as in the Aphalliate species, but 
in correlation with the development of an 
external copulatory organ, an open ciliated 
conduit became established, leading along the 
side of the body from the pallial termination 
of the sperm duct to the apex of the intro- 
mittent male organ; this open duct hecame gradually enclosed within 
the body, and now constitutes the vas deferens, a certain section of its 
course even yet, however, retaining an intermuscular course beneath 
Fig. 657. — Open ciliated 
external sperm-duct of Peiia 
coronata (highly magnified), 
(after Pelseneer). 
s.f. seminal furrow ; 7n. 
mantle ; f. fool. 
Fig. 60S. — Section through the 
prosialic portion of sperm duct 
Limmva /^w^r/I(^iull.), X 10, 
showing its glandular character. 
