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 H. 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. alholahris, H. 

 tridentata, H. dentifera, H. palliata, IT. arhorea, and 

 H. fallax, are alike ; JI. intertexta, H. gidaris, S. 

 suppressa, and H. ligera are also alike, except that the 

 two latter have but a single vesicle to the dart sac, while 

 the former have a pair. H. auricidata, H. texasiana, 

 and S. injleeta, are alike, and also iZ". thyroidus and H. 

 pulcJiella. 



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 



