492 Gross Anatomy of Campeloma. 



and VII. of Fig. 1, in the text). Again, as appears below, the shells 

 differ in certain particulars of corresponding dimensions. 



The male seminal duct is displayed throughout nearly its whole 

 length by clipping the mantle along the extreme left of the branch- 

 ial chamber. The vas defer ens superior (IV., Fig. 1) arises from 

 a point on the anterior left third of the testis (II., Fig. 1). This 

 latter organ is placed immediately under the 

 right duodenal fold of the intestine (I., Fig. 

 1). It is about three times longer than wide, 

 _ w and whitish in color. The vas deferens supe- 

 rior after passing anteriorly to a point near the 

 anal extremity of the intestine is suddenly bent 

 * obliquely backwards and traverses the floor of 

 the branchial chamber for a short distance, 

 but soon turns forward again at a somewhat 

 acute angle. At this point (III., Fig. 1) is the 

 prostate. The vas deferens inferior (V., Fig. 

 *' 1) is rather long, narrow, and nearly straight,. 



and is continued along the floor of the right 

 tentacle to the verge (VI., Fig. 1). The right tentacle thus becomes 

 an intromittent organ in the process of copulation. This tentacle 

 is somewhat flattened above, presenting, in cross section, an elon- 

 gated ellipse. It is somewhat less in length than its left fellow,. 

 and is rather more curved outwards. 



In the gravid female the gestatory sac (Plate VII., Fig. 5, c) oc- 

 cupies the greater portion of the body whorl on the right side. It is 

 readily distinguished in the living specimen by the greater deposit 

 of black pigmentary matter in its thin outer walls. Anteriorly the 

 sac opens into a rather small duct, the mouth of which is prolonged 

 into the branchial chamber about 2 to 2.5 millimetres (b, Plate VII.,. 

 Fig. 5). This duct is guarded at each extremity by rather power- 

 ful sphincter muscles. Anteriorly the walls of the gestatory sac 

 are slightly thicker and are modified into longitudinal folds or 

 rugse leading towards the duct. These possibly are of use in 

 guiding the extrusion of the young. 



During the summer and fall months, and often also in hiber- 

 nating specimens, the gestatory sac is crowded to distension with 

 young, in various stages of development (Plate VII., Fig. 5, c). 

 Those most anterior are, in early August, nearly or quite through 

 their prenatal growth, and are less closely crowded upon one another 



