10 INTRODUCTION. 
the central group of polar radiations, and, as will be seen from Fig. 4, 
E, F, G, the impression is that the polar radiations and the spindle 
contain the same number of fibers, which are continued uninterruptedly 
through the poles. But the continuity of the fibers is sharply inter- 
rupted by an achromatic plane at the nuclear membrane, through which 
the deeply staining (violet, by the Flemming triple stain) fibers pass 
from nucleus to cytoplasm. Whether the spindle fibers actually end 
at the nuclear membrane, or whether their substance only stains less 
densely there, was not determined. However, the phenomenon leaves 
the impression that the central body consists merely of the bases of the 
polar radiations closely crowded together. If the centrosome is an 
individual organ here, it seems that it must consist of a very thin, flat- 
tened disk, equal in breadth to the blunt end of the spindle. 
The poles of the spindle now separate farther from each other, 
whereby the spindle becomes straight. The individual chromosomes, 
eight in number, which are arranged in the equatorial plate, are sharply 
defined, and the nucleus has become somewhat elongated (Fig. 4, G). 
The polar radiations have again become fine elongated fibers, forming 
regular systems of sun-like radiations. 
As soon as the daughter chromosomes have reached the poles of the 
spindle the nuclear membrane disappears (Fig. 4, H). The fibers of 
the central spindle become now less sharply defined and broken in 
different places. Their number is also gradually diminished, their 
substance soon being indistinguishable from the immediately surround- 
ing cytoplasm. The polar radiations, however, form at this stage a 
more regular and sharply defined aster, owing to the outer rays bend- 
ing somewhat backward round the chromosomes (Fig. 4, H). The 
latter form a dense mass in which the individual elements are no 
longer to be distinguished. The centrosome is likewise not to be 
distinguished from the chromatin mass near which it lies. A nuclear 
membrane is now formed about each daughter nucleus, which appears 
as a small vesicle with the chromatin mass at the polar side (Fig. 4, I). 
With the further development of the nuclear membrane the free 
cavity of the nucleus increases in size. The chromatin mass begins to 
swell, and is gradually transformed into threads and lumps which are 
arranged, at first, mostly along the nuclear membrane, but soon 
become distributed through the nuclear cavity. A nucleolus now 
appears, and with the further growth of the nucleus the chromatin 
passes over into the netlike framework like that in Fig. 4, J, A. 
As soon as the nuclear membrane is formed, the polar radiations 
begin to disappear. In Hrysiphe they seem to be transformed into a 
granular mass (Fig. 4, J). Finally, when the daughter nucleus is 
