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8 THE CHICAGO ACADEMY OF SCIENCES. 
and finds an exit if 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 Lymnea 
stagnalis in Keferstein (taf. citi, 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 (pl. xxxiu, fig. 25) of 
Radix auricularia is almost identical, but his figure of Lymnea stagnalis 
(pl. 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 
Lymneas. 
b. THE, paw. — Plate wy 1. 
The mouth of Lymnza 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 Lymnea stagnalis. No such filaments, however, 
have been observed on the lateral jaws of American Lymnezas. 
There appears to be little variation in the type of jaw among 
