AND OF HYBRID PIGEONS. 
15 
PRIMARY SPERMATOCYTES. 
Early History. 
The primary spermatocytes or cells of the second sperma- 
togenetic period originate, as has been indicated, from the 
the cell-products of the last spermatogonial division through a 
process of growth. All transitional sizes between that of the 
spermatogonia and the comparatively large spermatocytes may 
be seen in practically the same order as that described by Len- 
hossek^ for the rat. In the new cells, the chromatin passes 
into the resting condition and an increase in bulk of both 
nucleus and the cytoplasm begins. The chromatin is arranged 
much as it was in the resting condition of the spermatogonia 
except that there is perhaps less distribution of the, chromatin 
granules along the periphery of the nucleus and the linin fibres 
are coarser (Fig. 6). 
The sphere first appears as an indistinct granular crescentic 
area closely applied to the nucleus, with the horns of the cres¬ 
cent so extended as to enclose more than half of the nuclear 
surface (Fig. 6, i.). As the young spermatocyte grows, the 
sphere also increases in size and become more and more 
rounded. 
From an early stage a minute centrosome is visible in the 
midst of the sphere substance. It is surrounded by a clear 
looking area which becomes more pronounced as the sphere 
grows older. Thus the developing cell gradually acquires char¬ 
acteristics of size, shape, and general appearance that differ 
considerably from those of the previous generations. 
At no point in this metamorphosis could I distinguish any 
nuclear element that might be identified positively as an 
achromatic nucleolus. Such a body, in fact, seems to be want¬ 
ing in all stages of the spermatogenesis. One or more bodies 
of var 3 dng size were often present but there was no evidence 
whatever to show that they differed in any way from the or^ 
dinary linin material. Certainly no such well marked object 
1. Loc. cit., p. 5. 
