30 
SPERMATOGENESIS OF NORMAE 
further could be determined concerning the centrosomes as they 
become lost to view at this point. 
At this stage of development there is no trace of the sphere 
in the cytoplasrn. The bubble-like structure mentioned above 
which originated in it, lies at what may now be designated as 
the anterior end of the developing spermatozoon. A flattening 
of the nuclear wall has occurred at the point of contact with the 
bubble and the latter becomes closely affixed or welded, as it 
were, to the nucleus (Figs. 20-24, hs.). The bubble-like portion 
develops ultimately into the head-spine (Figs. 22-27). 
Soon after the centrosome has penetrated the nuclear mem¬ 
brane, the elongation of the nucleus to form the head begins. 
At first only the anterior and posterior ends extend, but in a 
short time the whole nucleus begins to narrow. Concomitantly, 
the chromatic mass at the center begins to sprout out both 
anteriorly and posteriorly, and form a central core to the rap¬ 
idly lengthening nucleus (Fig. 23, ch.). 
As the process of elongation continues in the nucleus, a 
narrowing of the sides occurs to some extent, but when one 
takes into account the enormous elongation that takes place to¬ 
gether with the relatively slight diminution of the transverse 
diameter, it becomes evident that there must be considerable 
increase in the volume of the nucleus. 
The chromatin continues to lengthen with the extension of 
the nucleus and is visible as a heavy central chromatic filament. 
It extends entirely to the posterior end of the nucleus but falls 
a trifle short in front. After a time it becomes arranged in a 
more or less distinct wavy or spiral manner (Fig. 24, ch.). As 
the transformation progresses, the spiral design, although often 
very irregular, becomes more perceptible. Numerous linin 
fibers radiate out from this core of chromatin to the periphery 
of the nucleus, and frequently bridges or twigs of chromatin 
may be observed extending out along them to connect with the 
inner surface of the deeply stained nuclear wall. 
A splitting of the central core occurs sooner or later as 
indicated in Fig. 25, so that the main chromatin mass thereafter 
exists as two threads laid down in an irregular double spiral. 
This condition persists through the succeeding changes. 
The elongation of the nucleus ceases at about the time this 
