90 



region of the stomach. During all this length it receives 

 branches from the gonad and is coiled and folded in a very 

 characteristic manner. These convolutions become 

 more complex as the vas deferens passes forwards, and 

 finally it forms a tubular storing chamber in the region 

 between gonad and renal organ (fig. 54, V. def. 1 ). The 

 actual length of the vas deferens is several times the 

 distance from the tip of the spire to the end of that duct 

 in a straight line. After the convolutions the vas 

 deferens becomes again somewhat reduced in diameter 

 and, with fewer folds, passes forwards towards the 

 thickened body wall of the " neck " region. Just upon 

 reaching the pallial cavity, it turns in a spiral manner — 

 this part being again of somewhat greater diameter — and 

 then runs directly to the base of the penis under the body 

 wall, which forms the floor of the body cavity. 



The Penis is a permanent organ of very considerable 

 size, which arises somewhat on the right side of the neck 

 (fig. 54, Pen.). It is spatula-shaped, flattened, and 

 broadest at the distal extremity. Though capable of some 

 contraction, this tough muscular extension of the body is 

 so long that it would protrude from the shell were it not 

 for the fact that normally it is bent back and lies hidden 

 in the mantle cavity. A little distance from the end 

 there is a small tentacle at the apex of which the vas 

 deferens opens. The vas deferens, however, does not run 

 directly through the penis. It winds on itself in a spiral 

 fashion, running through a tunnel from the base of the 

 organ to its aperture on the tentacle. The male organs, 

 it will be seen, are comparatively simple, and no 

 accessory structures are connected with the vas deferens. 

 In some gastropods the penis has been found to undergo 

 seasonal variation in size — no trace of this has been 

 noticed in Buccinum. 



