SPECIAL ANATOMY. 225 



' pressa, it is wholly enveloped in a sheath derived from a 

 tubular offset from the duct of the generative bladder. 



The muscular tunic of the penis is thick and strong. 

 The internal lining mucous membrane usually presents a 

 number of large rugge, longitudinal and oblique ; fre- 

 quently there is but a single, large, longitudinal fold, as 

 in H. alternata, IT. albolabris, etc. At the point of en- 

 trance of the vas deferens there is generally one or two 

 pendant j valve-like folds of the lining membrane. 



In S. albolabris, II. tridentata, and H. onuItiUneata, 

 the surface of the membrane is everywhere distinctly 

 papillated ; in the others it is smooth. 



The penis of //. cellaria on the outside presents a row 

 of minute, round, glandular bodies. 



The retractor muscle is in all cases, except in H. soli- 

 taria, inserted into the summit of the penis, or into the 

 vas deferens near its termination in the latter. In the 

 excepted case, it is inserted into the side of the penis, 

 above its middle. In H. multilineata there are some 

 accessory fibres passing from the latter to the prepu- 

 tium ; in H. jjrofunda to the base of the penis ; in H. 

 albolabris, tridentata, etc. from the vas deferens to the 

 preputium. The penis joins at its base the cloaca. 



The ovary has the same general form and color as in 

 slugs, but rarely presents any thing more than a trace of 

 lobuli, usually having a uniform, homogeneous appear- 

 ance. The oviduct does not differ from that of the slugs. 

 Its neck is usually narrow, and of variable length, and is 

 joined at the lower part by the duct of the genital blad- 



voL. I. 28 



