100 
THIRTEENTH REPORT. 
these observations that the breeding- season for tills species extends over 
a period from about the first of August to the first of September. This 
is further strengthened by the examination of females which were not 
ready to lay eggs before the latter part of July and were without eggs 
in the middle of August. 
THE SPERMATOGONIA. 
As stated above there is in each follicle an apical cell around which 
are grouped the primary spermatogonial cells (Fig. 2). The nucleus of 
the apical cell is large and the chromatin is scattered through it in the 
form of fine granules. There may be one or more plasmosomes present. 
The nuclei of the primary spermatogonial cells are larger than those 
of the secondary spermatogonia. The chromatin contained within them 
consists of widely scattered granules. The nuclei are eccentrically 
placed; most of the cytoplasm, which is relatively large in amount at 
this stage, being on the side nearest the apical cell. 
In the actively dividing secondary spermatogonia the chromosomes, 
when in the equatorial plate, appear as more or less curved rods (Fig. 3). 
They are rather evenly distributed about the plate with the largest at 
the periphery. The chromosomes vary considerably and it is possible to 
select pairs of them of approximately the same size and shape. This, 
however, cannot be done with certainty for all of them. There is a large 
horseshoe shaped chromosome (Fig. 3x) which always lies at the edge of 
the plate, and for which there is no mate; this is the accessory chromo- 
some. 
The autosomes split longitudinally in the spermatogonial divisions. 
The accessory chromosome also splits longitudinally, and in favorable 
sections it can be seen in metapliase, projecting slightly from the plate 
(Fig. 4x). It lags behind the rest, one-half passing to either pole of 
the spindle’. The two long arms can be seen stretching toward each other 
after the autosomes have reached the poles (Fig. 5). 
The chromosomes are so closely packed in the spermatogonial plates 
that they can seldom be counted with accuracy. Furthermore there are 
relatively few spermatogonial nuclei in the proper stage for the deter- 
mination of the number of chromosomes. Because of these two facts the 
number could not be determined with certainty but there are probably 
thirty-seven or thirty-nine in the spermatogonia. 
GROWTH PERIOD OF THE PRIMARY SPERMATOCYTES. 
During (lie telophase of the last spermatogonial division there is a 
diffusion of the chromatin within the nucleus. At the earliest stage 
there is no spireme, the chromatin being scattered throughout the nucleus 
in the form of fine, granules (Fig. 6). A spireme then appears with the 
chromatin granules distributed evenly upon it. At the intersections of 
the thread the granules appear somewhat condensed. The spireme at this 
time has no definite position (Fig. 7) ; soon, however, it assumes the usual 
polar arrangement (Fig. 8). The thread or threads are apparently fas- 
tened to one side of the nuclear wall, and the loops extend out into the 
nucleus from this place of attachment. The loops are fastened to the 
distal pole of the nucleus, as determined by the position of the greater 
part of the cytoplasm. It was not possible to count the loops of the 
