228 INTRODUCTION. 
but longer. Into the summit of the dart sac is inserted 
a retractor muscle, originating from the angle formed by 
the division of the duct of the genital bladder into two 
parts. Opening into the tube which leads from the penis 
to the cloaca, in H. Berlanderiana, is a cylindrical, 
curved, muscular organ, about one-half the length and as 
thick as the penis, which is probably a dart sac, although 
in the specimen dissected no dart was found. In II. con- 
cava, opening into the cloaca, is a short, rounded, muscu- 
lar cavity, probably a dart sac, which, however, in the 
individuals dissected, were also destitute of the organ. 
The cloaca, or common receptacle of the termination 
of the male and female organs of generation, is a short, 
wide, muscular tube, holding no relationship with the 
length of the penis, and opening exteriorly on the right 
side of the head. 
In many species of Helix, the anatomy of the genera- 
tive apparatus is so very similar, that they appear to 
differ in nothing but size. Thus, H. albolabris, H. 
tridentata, II. dcntifera, H. palllata, H. arborea, and 
H. falla.r, are alike ; II. intertexta, H. gularis, H. 
supprcssa, and H. Ugcra are also alike, except that the 
two latter have but a single vesicle to the dart sac, while 
the former have a pair. //. awriculata, II. tcxasiana, 
and H. inflecta, are alike, and also II. ihyroidus and H. 
pulcliella. 
It is a very remarkable fact in the special anatomy of 
the generative apparatus of the genus Helix, that while 
the flagellate form of the penis and those accessory 
