226 INTRODUCTION. 
der, to form the vagina. In H. concava and H. multi- 
lineata, the neck is long, dilated at its lower part, and 
strongly muscular, and its internal surface presents a 
number of longitudinal rugae. In H. profunda and U. 
fuliginosa, it is long, cylindrical, and strongly muscular. 
The genital bladder, constantly existing, presents con- 
siderable variation in the form, size, and length of the 
duct. It is generally subrotund, oval, or pyriform in 
shape, and large. In H. solitaria the duct is wide, as 
long as the oviduct, and dilated at its lower part. In H. 
perspectiva it is as long as the oviduct, and narrow. In 
II. altemata, II. lie/era, II. intertexta, II. concava, H. 
suppressa, and H. gularis, it is rather more than half 
the length of the oviduct. In the remaining species gen- 
erally, the bladder reclines upon the lower part of the 
prostate gland, and its duct is about the length of the 
neck of the oviduct. In II. multilineata it does not 
reach the prostate gland, and so gradually passes into its 
duct as to be a mere, long, coecal tube. In H. her- 
landeriana the duct of the bladder is as short as that of 
Arion. Usually, the surface of the bladder is smooth ; 
in M. profunda and H. exoleta it is transversely folded ; 
in H. fuliginosa it is regularly, longitudinally folded. 
In H. concava and H. multilineata, the duct of the 
bladder at its termination dilates, and is strongly muscu- 
lar. In H. solitaria the lower third is dilated. In II. 
fuliginosa and H. profunda, it is strongly muscular the 
greater part of its extent. In //. albolabris, H. palliata, 
II. tridentata, etc. it is dilated to the size of the bladder, 
