368 REPRODUCTIVE ORGANS — IIAPLOSTVLA, ETC. 
Darts may be found within the dart-sac at all times of the year, 
but some species are much more liable than others to lose them, and 
if lost just prior to hibernation, it is probable that their renewal will 
be delayed until spring, but in Trlckutoxon, an exotic genus of slugs, 
the darts are permanent and are even furnished with chitinous sheaths. 
The tfypsobela or love-darts, according to the greater or lesser 
modifications they display, may for purposes of study be conveni- 
ently grouped in four sections, based upon the degree of complexity 
attained by the supporting lateral blades, viz., Haplostyla, Dispatho- 
styla, Tetraspathostyla, and Heterospathostyla. 
The Haplostyla (dvrA-ois, simple; smAos, pillar) 
embrace those species which possess a round and 
simply subulate dart, without any strengthening 
accessory blades or buttresses or any distinct apical 
developments or definite basal rod-like ornament- 
ation or enlargement ; these simply formed or 
primitive darts are often paired, the stylophores 
or dart-sacs occupying coiTespouding positions at 
opposite sides of the vagina. 
The Dispathostyla (dvo, two ; cnrddi), a blade ; ?ti>Aos, a pillar) 
possess darts of the simply subulate Haplostylous type, with 
the addition of a pair of sti'engthening blades or buttresses placed 
at opposite sides of the weapon ; 
these Idades may be restricted to 
the free end which therefore be- 
comes more or less enlarged, and 
forming in its extreme develop- 
ment a tlattened lanceolate head, 
as seen in Helix lapicida. 
In its more primitive form it 
illustrates the origination of a pair 
of lateral blades or buttresses near 
the apex ; these, however, often do 
not ac(iuire great prominence, but 
sometimes extend the length of the 
dart ; the most rudimentary form 
of the dart is exhibited by Helix 
aipemta, but Helix virgata shows 
the lateral apical blades as distinct formations. 
Fig. 677. Fig. 678, 
Fig. 677. — Gypsobelum or love-dart of 
Helix virgata Da Costa, X 8, with section 
showing the paired lateral blades, and illus- 
trating the Dispathostyla. 
Fig. 678. — Gypsobelum or love-dart of 
Helix lapicida L., X 8, with section of 
head, showing the exaggerated develop- 
ment of the paired lateral blades and their 
assumption of the lanceolate form. 
Fig. 670. — Gypsobe- 
lum or love -dart of 
Helix p^ilchclla Mull., 
X20, showing the primi- 
tive simplicity of the 
weapon, and illustrating 
the Haplostyla. 
