226 Henry Lesie Ossorn, 
IT) The female organs. 
The ovary is always located on the right side directly under 
the diaphragm and on the level of the center of the ventral sucker 
(see Fig. 5). It is elliptical and varies in length (in thirteen cases 
killed under compression and mounted in balsam) from 0.1 mm to 
0.3 mm. Its width ranges from 0.07 mm to 0.13 mm. It consists 
of two portions which (Fig. 50), from the point of view of the con- 
tained ovarial cells, are very distinct, viz. an anterior part con- 
taining very large cells in close relation with the beginning of the 
oviduct and a deeper posterior portion in which the cells are small 
and more immature. The ovary is enclosed in a very thin but per- 
fectly distinct wall in which much flattened nuclei can be seen at 
wide intervals. STAFFORD considers this layer in Aspidogaster to be a 
flattened parenchyma. I have seen nothing in Cotylaspis to indicate 
its source. The wall contains some muscle fibers, but they are uot 
very numerous. The cells inside this wall (see Fig. 48) do not form 
any distinct epithelial layer. As is usual among the trematodes the 
cells show stages of development toward the oviduct. I have not 
traced the stages of ovigenesis completely, but the following obser- 
vations have been made. There is posteriorly a peripheral layer 
of cells (Fig. 52) in contact with the outer wall. They are small, 
have a large nucleus 0.006 mm in diameter, and consist of a nuclear 
membrane, scattered and indefinite chromatine in small grains, and 
a nucleolus. The nucleus nearly fills the cell and the cytoplasm is 
small in amount. These cells bear a close resemblance in size, 
position and structure of the primitive cells of the spermary. The 
center of this portion of the ovary is occupied with a type of cell 
shown in Figs. 51 and 52, doubtless derived from cells of the sort 
just described, which show different stages of mitotic division. In 
the center of the ovary we find much larger cells (Fig. 53) with a 
nucleus of a diameter of 0.01 mm, in which a distinct membrane 
encloses a large nucleolus which is a center of a system of minute 
threads on which minute grains of chromatine are arranged. These 
cells have a large amount of cytoplasm of a fine-grained homogeneous 
texture completely filling the faint but definite cell membrane. They 
are much crowded which results in the production of the characteristic 
wedge shape, and fill this region of the ovary completely. The cells in 
the anterior part are very large measuring 0.033 mm in length. The 
nucleus is large (0.015 mm in diam.) and the nucleolus is very large, 
