66 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
of connective-tissue cells, which are easily distinguished by their 
relatively small size and deeply staining nuclei. ‘These cells extend 
proximally along the center of the follicle for some distance, forming a 
more or less distinct longitudinal rachis. Proximal to the primary 
spermatogonia are the secondary spermatogonia arranged in groups, 
which are surrounded by a thin but distinct membrane, composed of 
connective-tissue cells, each group constituting a spermatocyst. Each 
spermatocyst remains distinct from its fellows from the time of its 
formation until the spermatozoa become mature. ‘The spermato- 
cysts are arranged in regular sequence from the distal to the proximal 
end of the follicle, so that successively older stages in the development 
of the germ cells are encountered as one goes toward the proximal 
end. ‘This is, of course, due to the fact that existing cysts are con- 
tinually being forced toward the vas deferens by the formation and 
growth of new cysts at the distal end; thus cysts which are formed at 
about the same time come to occupy neighboring positions in the 
follicles. 
Surrounding the whole is a distinct follicular wall, in which flattened, 
deeply staining nuclei can be distinguished at intervals. 
In Steiroxys the structure of the testis is much the same, except that 
in the later stages a single spermatocyst may come to occupy the entire 
cross-section of a follicle. 
2. THE SPERMATOGONIA. 
A. Daissosteira carolina. 
The primary spermatogonia (Plate 1, Fig. 5) are large rounded 
cells situated at the distal end of the follicle. Each cell contains a 
large eccentrically placed nucleus, which is usually more or less 
irregular or lobulate in shape, the nuclear membrane often extending 
out in the form of short sacculations, like the fingers of a glove. This 
irregular or polymorphic form of the nucleus is more marked in the 
secondary spermatogonia, where it will be considered more at length. 
On one side of the primary spermatogonia the cytoplasm is much more 
abundant than elsewhere, and adjacent to this cytoplasmic mass the 
nucleus is flattened or concave. At the height of the resting stage 
the chromatin is distributed through the nucleus in the form of fine 
granules suspended in the linin network. At intervals, especially at 
the intersections of the linin teres, the chromatin granules tend to 
aggregate in irregular masses. In addition, the nucleus contains one, 
