40 
SPERMATOGENESIS OP NORMAL 
ceive chromatin from both equators and consequently from 
both parent species. Each of the other cells will contain ex¬ 
clusively chromatin from different ones of the two spindles, 
hence, each will represent but one of the two parent species. 
Where two complete and separate spindles occur, of course, it 
is possible that none of the four resulting cells will be of the 
mixed tpye; each may be pure. The unequal division of 
individual chromosomes which sometimes occurs would tend to 
introduce chromatin of the opposite species into many other¬ 
wise pure cells. 
ABNORMALITIES IN THE STRUCTURE OF SPERMATOZOA. 
The misshapen spermatozoa that come under this heading 
were present only in the sterile hybrids. In such forms there is 
a curious varicosity or swelling about the middle of the sper- 
matozoan head (Fig. 40) that attracts the attention immediately 
when the objects are examined under the microscope. This 
enlargement seems to be almost universal among the sperma¬ 
tozoa of sterile hybrids and is sufficient of itself to produce 
sterility, for such a malformation would prevent its possessor 
from entering the egg. In a very few instances what appears 
to be a normal spermatozoon can be observed among the de¬ 
formed ones and it is possible that if these reached a suitable 
egg, fertilization might result. Although the odds against them 
are very great, there is no reason apparent why they should 
not occasionally reach an egg and fertilize it. 
A study of the development of the spermatozoa reveals the 
fact that the bead-like enlargement results from the incomplete 
development of the nucleus to form the head. The two ends 
of the nucleus sprout out like the filament of a germinating 
spore and grow for a short distance, but the remainder of the 
nuclear wall retains its original form and position (Figs. 41, 42). 
The arrangement of the chromatin is very irregular. A deeply 
staining mass is visible in the bulb-like swelling, from which 
thick threads spring out forward and to the rear (Figs 41, 42). 
Figs. 43 and 44 show irregular forms of heads in which the 
protrusion or outgrowth of the nuclear wall has been in other 
directions than in the longitudinal axis. Such extreme forms 
are comparatively rare. 
