22 
SPERMATOGENESIS OE NORMAL 
(Fig. 10). Small astral radiations are also visible, but they are 
very scant and can be traced only a short distance from the 
centrosome. 
The next step is the disappearance of the nuclear membrane 
and the attachment of the chromosomes to the spindle. It was 
impossible to follow out the details of this process. The 
change must take place very rapidly for it is very difficult to 
find it in progress. There is a thickening of the spindle fibers 
as the rearrangement comes about until a very prominent 
spindle is formed (Fig. 11). The fibers, eight in number, are of 
comparatively enormous size. The whole appearance of the 
spindle is very different from that seen in the spermatogonial 
division (Fig. 5). The fibers are much coarser and the spindle 
as a whole is longer and not so broad (cf. Figs. 5 and 10). The 
number of fibers, it will be observed^ is the same as the number 
of chromosomes. 
The chromosomes stand out prominently from the spindle 
at first, as if attached by only one edge, but they finally become 
more closely affixed. Considerable practice is required before 
any satisfactory results can be obtained in counting. Inasmuch 
as the chromosomes do not lie in one plane, careful manipula¬ 
tion of the fine adjustment of the microscope is necessary and a 
large number of cells must be examined. Even then the re¬ 
sults are not always as conclusive as one might wish. In the 
present case, nevertheless, I think there is little doubt that eight 
is the correct count. 
In dividing, the chromosomes always elongate toward the 
poles and break transversely at the equator. They may stretch 
to a considerable distance before the final rupture occurs. 
Often the chromatin part of the ring divides early and the two 
daughter chromosomes remain connected by a thick band of 
the achromatic substance which encases them (Fig. 12). These 
connecting strands or tubes of achromatic material, indeed, per¬ 
sist generally until the chromosomes have extended quite to the 
two poles. As soon as the division of the chromatin occurs, 
the free ends of each of the newly formed chromatic loops 
almost invariably fuse together immediately to form a ring or 
vesicle which is smaller and thinner than the original mother 
chromosome (Fig. 12). 
