32 SPECIAL ANATOMY OF THE TERRESTRIAL 



is strongly muscular, and internally presents a number 

 of regular, longitudinal folds, sometimes undulated at the 

 sides, extending to the lining of the bladder in the form 

 of line-like plicae. In H. ligera, H. intertexta, H. 

 gularisy and II. suppressa, an offset from the duct of the 

 bladder passes down, and encloses the penis, dart sac, 

 and cloaca. 



The vagina, or common duct of the oviduct and duct 

 of the genital bladder, holds no correspondence with the 

 length of the penis ; it is always shorter, usually not 

 more than one-third the length, and is also narrower. 

 In II. faligiiiosa^ it is surrounded by a thick, glandulous 

 body. 



In II. ligera, H. intertexta, H. gularis, and II. sup- 

 pressa, there exists, opening into the cloaca, a curbed, 

 cylindrical, strongly muscular dart sac, longer and nar- 

 rower than the penis. The bottom of the tube, for one- 

 fourth the length of the latter, is occupied by the papilla 

 from which arises the dart. The muscular layer, for 

 more than half the length of the tube, at the middle of the 

 latter, closely envelops the dart, and terminates abruptly 

 below in a sort of papilla, from which the point of the dart 

 projects into the lower part of the tube. The dart is a very 

 long, narrow, curved, cylindrical, tubular, flexible, calca- 

 reous spiculum, terminating in a sharp, spear point. At 

 the base of the dart, there opens into the dart sac, in II. 

 ligera and II. suppressa, a single, short, pyriform follicle, 

 the simplest homologue of the multifid vesicle. In //. in- 

 tertexta and II. gularis, there is a pair of such folUcles, 



