370 
REPRODUCTIVE ORGANS — STYLOPHORE. 
into the vagina below the aperture of the digitate glands, and 
is composed of a thick outer layer of transverse and longitudinal 
ninscle tihres, which are thinnest at the summit of the sac, and facili- 
Fig. 681. 
Fig. 632. 
Fig. 633. 
Fig. 684. 
Dart sacs of different species of Helices, with the vaginal digitate glands, showing the evolution 
from the multiple to the simpler single sac. 
Fig. 681. — Bifid laterally paired sacs of Helix ntfcsccns Penn., X 3. 
Fig. 682. — Bilaterally paired sacs of Helix itala L., X 3. 
Fig. 683.— Unilaterally paired sacs of Helix fusca Mont., X 3. 
Fig. 684. — Dart sac or stylophore of Helix pomatia L. 
tate its eversion; the more delicate and glandular inner layer is 
adherent to the outer envelope, it is often deeply pigmented and 
secretes a viscous lubricating fluid. 
For convenience the dart sac of the British species may be sepa- 
rated into two groups, in which the teliferons sacs are single or 
paired; both, however, may he more or less completely divided, giving 
an e.xternal appearance of double and (j^nadrnple sacs, but only the 
outer sacs develop darts, the subsidiary additional sacs which always 
lie nearest the vaginal passage showing no indication of ever having 
done so, and it is not improbable that these auxiliary sacs may be 
a modified form of the coronal glands present in Zonitoides. 
In Zonitoides the lubricant 
glands are concentrated in the form 
of an oval pouch protruding 
externally near the apex of the 
dart sac and opening therein ; 
this peculiar glandular outgrowth 
represents a remarkable feature 
strikingly developed in the exotic 
genus Ariophmtd, in which it 
takes the form of a circlet of 
similar outgrowths around the sub- 
terminal portion of the sac ; such 
apical glandular developments have been distinguished by Pilsbry 
as coronal glands. 
Fig. 685. — Reproductive organs of Zoni- 
toides excavata (Bean), X 10, showing I he 
glandular outgrowth or coronal gland of the 
dart-sac (after photo, by W. Moss). 
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. 
