8 THE CHICAGO ACADEMY OF S< [EN< ES. 



and finds an exit in the anus (8) within the mantle cavity not far from 

 the orifice of the vagina. The last part of the intestine is somewhat 

 enlarged to form the rectum (7). The digestive gland is very large, 

 filling completely all but the last whorl of the shell, and is dark brown 

 in color. It is composed of two lobes, one occupying the apical whorls 

 and the other (larger) filling the last whorl just behind the heart. 

 It opens by a number of large ducts into the intestine, and into the 

 pyloric portion of the stomach. The digestive gland (9) is well sup- 

 plied with blood vessels, which ramify in every direction, forming a 

 complicated plexus. The digestive gland is scarcely analogous to the 

 liver of vertebrate animals, as it contains a diastatic ferment, which 

 converts starchy matter into glucose. It is probably comparable to the 

 pancreas in the vertebrate animals. 



In general the alimentary tract agrees with the figures published 

 by European authors. The figure of the general anatomy of Lymncea 

 stagnalis in Keferstein (taf. ciii, fig. 7) shows this tract very like that 

 of the present species, except that no division into crop, stomach and 

 gizzard is indicated. Moquin-Tandon's figure (pi. xxxiii, fig. 25) of 

 Radix auricularia is almost identical, but his figure of Lymncea stagnalis 

 (pi. xxxiv, fig. 18) differs in the form of the stomach, which does not 

 show the divisions indicated above. 



There appears to be little variation in the digestive system of the 

 Lymnseas. 



b. the jaw. Plate VI. 



The mouth of Lymnsea is somewhat T-shaped when in repose. 

 The upper portion is armed with a strong, horny organ called the 

 superior jaw (A, 1) which is wide and low, arched dorsally and trilobed 

 ventrally, the center lobe being more or less acute, while that on either 

 side is simply rounded. The ends of the jaw are frequently somewhat 

 produced. The anterior face is striated and the whole jaw is generally 

 brownish in color. The jaw is fastened to a short cartilage and is 

 protracted and retracted by a set of muscles. 



The lateral jaws (A, 2) emargine the sides of the mouth and are 

 very long and narrow and curved at the superior end, where they are 

 attached to a wide cartilage. Before being spread out, as in the figure, 

 the lateral jaws appear as a narrow black edging to the mouth, the 

 cartilaginous portion of the upper part being bent backward within 

 the mouth. Butterell (1880) mentions certain filaments which cover 

 the lateral jaws in Lymncea stagnalis. No such filaments, however, 

 have been observed on the lateral jaws of American Lymngeas. 



There appears to be little variation in the type of jaw among 





