MITOSIS. II 



continuous thread but passes from the network condition directly into that 

 of a group of chromosomes. Such a group is, however, properly called 

 a monospireme. 



The centrosomes, in moving apart from one another, travel along 

 the nuclear membrane to points 90 from their original position. Thus 

 if before division the centrosome was on one side of the nucleus, now the 

 two centrosomes into which it has divided will be found one at either end 

 of the nucleus. Fine fibrils extend between them as they separate, con- 

 stituting the central spindle. Outside of these, there are other fibrils 

 passing from the chromosomes to the centrosomes (Fig. id). These 

 fibrils, which are sometimes derived from those of the centrosphere and 

 sometimes from the linin framework of the nucleus, are known as mantle 

 fibrils. Toward the end of the prophase the nuclear membrane disappears, 

 together with the nucleoli. 



M eta phase. The V-shaped chromosomes become arranged about 



Polar radiation. Xuclear spindle. 



FIG. ii. EARLY METAPHASE: Mox- Fir,. i>. METAPHASE: DIVISION: 



ASTER. OF THE CHROMOSOMES. 



the equator of the spindle in such a way that their apices point toward the 

 axis of the spindle and their free ends radiate from it in all directions, Fig. 

 ii. At either apex of the spindle is the centrosome surrounded by the 

 centrosphere, the radiating fibrils of which are now called polar radiations. 

 If the cell at this stage is view r ed from one of its ends or poles, the chromo- 

 somes together constitute a single star and this mitotic figure is accordingly 

 called the monaster. Fig. 15 shows the monaster both in side and polar 

 views. 



In the prophase, before the chromosomes have formed, the convoluted 

 thread of chromatin is sometimes seen to be split longitudinally into 

 halves. During the prophase, therefore, each V-shaped chromosome 

 may consist of parallel portions which remain together until the monaster 

 is complete. Then, beginning at the apex of the Y, the halves of each 



