IO 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 Erysiphe they seem to be transformed into a 

 granular mass (Fig. 4, J). Finally, when the daughter nucleus is 



