150 RAYMOND BINFORD 
are further along in their development than those at the other 
end. Thus in one end of a cavity the cells may be in the early 
prophase of the division of the spermatocytes of the first order 
while in the other end they have reached the spermatid stage. 
All the stages in the transformation of a spermatid into a sper- 
matozoon may be found in passing from one end of a tubule to 
the other. ; : . 
At the center of the upper border of figure 4, p.s., there is one 
cell with a large nucleus. This is one of a single row of cells 
along the side of the tubule which may be called the primary 
spermatogonial cells since they, by division, give rise to a new 
lot of spermatogonia. Near the top of figure 3, p.s., we find 
a similar cell. The cells forming the crescent-shaped region are 
in this case not so far advanced as in figure 4. Figure 1 repre- 
sents a tubule, the largest portion of which is filled with sperma- 
tids which have already entered upon their transformation into 
spermatozoa. In the upper portion of the drawing we have an 
early stage in the formation of a new batch of spermatogonia. 
There are four large spermatogonial nuclei surrounded by many 
epithelial nuclei and a considerable amount of cytoplasm. Deli- 
cate cell walls cutting out the cytoplasm which belongs to each 
spermatogonial cell can sometimes be made out at this stage. A 
later stage in the multiplication of these cells is shown in figure 
2. <A large nucleus, p.s., near the middle of the convex border 
of the spermatogonial mass, doubtless marks the position of the 
row of primary spermatogonial cells which will persist unmodified 
to form, at a later period, another lot of spermatogonia. The 
largest cavity of this tubule contains spermatids well advanced 
in their transformation into spermatozoa. In figure 3 the mass 
of spermatogonial nuclei is still further enlarged. Indeed most 
of them have probably reached the spermatocyte stage. The 
spermatocytes in the early prophase of the first maturation 
division are shown in figure 4. By putting these observations 
together we may determine the approximate order of events in 
the genesis of the spermatozoa. 
