REPRODUCTIVE ORGANS — APPENDIX AND UTERUS. 
363 
From the naked and permanently external organ of the Strep to- 
neures, many lines of variation have arisen, leading to the form 
concealed within an ample sheath or sac and capable of retraction or 
protrusion through the genital orifice, a form especially characteristic 
of the Euthyneura ; or the typical intromittent organ may itself 
become atrophied and its function be performed by the inversion of 
the penis sheath as in many Limnww, while in the Arionidw the 
sheath also becomes lost, the epiphallus opening directly into the 
genital vestibule, and the intromittent function being relegated to 
the vagina and spermatheca duct. 
In Helix acuta the penis sheath contains a perforate calcareous 
body to which the epiphallus and retractor are fixed. Our Zoni- 
toides present a similar feature formed, however, by the apposition of 
two calcareous but somewhat dissimilar hollowed or channeled plates. 
Fig. 663. — Proximal portion of sexual 
organs of Zonitoides excavata (Bean), X 10, 
(from a photograph by Mr. W. Moss), 
showing the position and character of the 
calcareous penial plates and the organization 
generally. 
st. stylophore or dart sac, showing natural 
position of dart and character and position 
of the coronal gland, c.gl. ; p.s. penis sheath 
with calcareous channeled plates; vag, vagina; 
sp. bifid spermatheca duct. 
a.g. 
Fig. 664. — Reproductive organs of 
Helix acuta Miill., X 2, more especially 
to show the position and character of the 
appendix. 
a.g. albumen gland ; ot. ovotestis ; 
h.d. hermaphrodite duct; ov. oviduct; 
V. vagina ; s.d. sperm duct ; v.d. vas 
deferens ; ep. epiphallus ; p.s. penis 
sheath with retractor ; sp. spermatheca. 
The Appendix is an external adjunct to the reproductive system, 
opening into or near to the penis sheath ; its function is uncertain, 
but I do not regard it as improbable that its affinities are with the 
semi-independent flagellum found in Bithjnia, Buliminus, etc., and 
other groups which have a similar position in relation to the penis. 
The Uterus or Glandular Oviduct is the convolute and spacious 
duct with sacculate glandular walls through which the ova pass after 
fertilization, becoming well developed and surrounded by the secre- 
tion of its walls. In the hermaphrodite species it is more or less 
intimately united with the prostate or glandular sperm duct, from 
