360 K. MASUI: 
III. The Primary Spermatocyte. 
A. GRowTH PERIOD. 
Resting stage :—The daughter cells resulting from the last division of the 
spermatogonia are the primary spermatocytes and these immediately go 
over to form the resting stage. The primary spermatocytes in the resting 
stage rarely appear in the testes of young animals (Fig. 2). These are always 
in contact with the spermatogonia arranged directly within the wall of the 
tubule and considerably smaller than the latter cells (Fig. 3). The nucleus 
of the spermatocyte in the resting stage usually contains, like that of the 
spermatogonial cells, one large chromatin nucleolus and several small chromatin 
masses (Fig. 13). The chromatin nucleolus has an indistinct contour and 
stains intensely with iron-haematoxylin, the same colours staining the small 
chromatin masses similarly (Figs. 13, 14). The cytoplasmic structures, with 
exception of the idiozome, can not be identified (Fig. 13). In the succeeding 
stage many small chromatin masses begin to appear (Fig. 15). 
Synaptic stage :-—After a brief resting stage of the primary spermatocyte the 
chromatin soon condenses into an apparently continuous, slender filament, and 
passes to the leptotene stage (Fig. 16‘. The leptotene threads later begin to: 
converge towards one side of the nucleus, while the bulk of the cell gradually 
increases to about twice the size of the resting primary spermatocyte (Fig. 17). 
Finally the chromatin filaments converge at a pole of the nucleus where the 
idiozome is situated (Fig. 18), and at the same time the nuclear wall expands. 
leaving a clear space on the other side of the nucleus. Im such cells, as shown 
in Fig. 18, we can clearly see the parallel arrangement of the chromatin threads. 
The centrosome can not be traced within the idiozome at this stage. 
Near the end of this stage the whole mass of the chromatin threads. 
gradually moves toward the center of the nucleus, the large clear space thus 
gradually disappearing, while the nuclear wall becomes spherical and more: 
clearly defined (Fig. 19). 
During the synaptic stage the chromosome nucleolus is invariably located 
at the converging point of the chromatin threads and retains its sharp contour 
but is never found in the clear area (Figs. 17, 19). 
