Gross. Anatomy of Campeloma. 497 
above the base of the left tentacle. The chamber is somewhat less 
in size in the gravid female than in the male, a fact the explanation 
of which probably lies in the distension of the gestatory sac and 
its consequent encroachment upon the branchial space. The cham- 
ber narrows rapidly posteriorly, and hecomes laterally constricted, 
From its upper and left side walls is pendant the ctenidium 
(Plate ? Fig. 5, Br). This organ consists of a single row, contain- 
ing a great number of thin elongately triangular plates, connected 
above with the branchial vein. The right edge and lower extrem- 
ity of each plate is free, and each is constantly bathed with water. 
The plates become smaller as the rear end of the chamber is reached ; 
they are yellowish white in color, and are furnished with abundant 
cilia. The blood, which is aerated in these plates, is white. 
The attention of students with proper appliances at command is 
directed to these molluscs in respect to their embryology, nervous 
system, minute anatomy of the reproductive organs, myology and 
circulatory system. Only the crudest observations on these points 
were possible under the conditions which were presented to me, and 
such facts as were ascertained are repressed in the hope that some 
other one will be able to complete the work here outlined. 
Explanation of the Plate.—X 4. All the figures, save Fig. 2, 
are drawn from the female. The mantle is clipped along the left 
margin of the branchial cavity. 
Fig. 1. Female, Fig. 2, male individual. 
Fig. 3. A single transverse row of teeth. 
Fig. 4. Odontophore, natural size and very greatly enlarged. 
Fig. 5. Anatomy of the branchial cavity with related organs. 
a. tvectum and anus, 
b. The opening of the gestatory sac, c. 
br. The ctenidium. 
The figures on the plate were drawn by Mr. H. A. Pilsbry 
from dissections made by him. Those in the text are drawn, some- 
what diagrammatically, by the author, from nature. 
