REPRODUCTIVE ORGANS — SPERMATHECA AND ATRIUM. 
371 
The Spermatheca (o-n-epfxa, seed ; Oeya-, a sheath) i.s a stalked vesicle, 
developed in the Euthyneures and some of the Streptoneures as an 
addition to the female organs to receive the Spermatophore or seminal 
fluid from the male organs of its partner. 
Usually it takes the form of a vaginal or vestibular diverticulum, 
■with a terminal sac-like enlargement ; in Pupa, Clausilia, and certain 
groups of Helices the stem develops an auxiliary diverticulum, known 
as the copulatory branch (see fig. 323, page 160), which, when w'ell 
developed, flir exceeds the length of the primary duct, and sometimes 
acquires a sac-like termination. 
A most remarkable variation from the typical spermatheca, shared 
by the North American Gastrodoutse, is found in Zonitoides, in which 
the stem becomes divided or cleft, the chief or most capacious duct 
opening into the penis sheath and the other in the normal position 
upon the vagina; a similar feature is said to be exhibited by Clausilia 
and Balea and appears to culminate in the African Trochommpha, in 
which Pfeifer could find no external opening for the male organ, the 
cleft spermatheca duct being therefore assumed to be a contrivance 
to ensure self fertilization. 
Fig. 686. — Reproductive organs of Zoni- 
toides excavata (Bean), X 3, showing the 
bifid spermatheca duct. 
ot. ovotestis ; h,d. hermaphrodite duct ; 
a.g. albumen gland ; s.d. sperm duct ; p s. 
penis sheath; oz>. oviduct; v. vagina, with 
vaginal gland ; sp. spermatheca with divided 
duct ; st. siylophore or dart sac. 
Fig. 687. — Reproductive organs of 
Arion circuinscriphis X 2, show- 
ing the vestibular gland. 
of. ovotestis ; a.g. albumen gland ; s.d. 
sperm duct ; v.d. vas deferens ; ep. epi- 
phallus ; cn’. oviduct ; sp. spermatheca, 
with its retractor ; v.p. vestibular gland. 
The Atrium {atrium, an entrance-hall) or Vestibule, is the thick- 
walled and often longitudinally ridged spacious cavity opening to the 
exterior and wdthiu which the various organs of the reproductive sys- 
tem converge ; it may also contain the Sarcobelum, or excitatory organ, 
and is enveloped exteriorly in A riun by a compact and dense glandular 
pad, whose secretions are discharged directly into the vestibule. 
