96 HYPERTROPHY, HYPERPLASIA, METAPLASIA, REGENERATION. 



somewhat flattened cluster or wreath between the polar bodies, lying in a 

 plane at a right angle to a line passing between the latter. ' While this 

 mass of chromosomes sometimes called the monaster has a stellar or 

 wreath-like appearance when seen from the side, it is more band-like 

 when viewed in profile (Fig. 30, 3 and 4). 



Between the polar bodies and across the monaster there may now be 

 stretched a bridge or spindle of delicate fibrils resembling those about the 

 centrosome in the polar bodies. 



This fibril -spindle, together with the polar bodies, is called the achro- 



FlG. 30. -PHASES OF MITOSIS. 



1. Resting cell. 2. Spireme phase : the centrosome has divided, the polar body is seen above ; the nu- 

 clear membrane has not yet disappeared. 3. Monaster phase : the polar bodies have arranged themselves 

 on either side of the monaster here seen from the edge. 4. The monaster seen from the side. 5 and 6. 

 Blaster phase : the chromosome clusters have separated and the achromatic figure is seen : in 6 the seg- 

 mentation of the cell body has begun. 7. The completion of the nuclear division and segmentation of the 

 cell body. 



matic figure in distinction from the structure formed from the chromatin 

 which stains with nuclear dyes, and is called the chromatic figure. 



The whole complicated structure composed of both the chromatic and 

 achromatic substance constitutes the mitotic figure. 



Now each chromosome splits lengthwise into exactly equal parts. 

 These parts separate into groups which pass to the polar bodies at op- 

 posite ends of the spindle. This is sometimes called the diaster phase of 

 mitosis (Fig. 30, 5 and 6). 



Corresponding to the division of the chromosomes into equal parts, 

 the cell body divides, each part containing one of the groups of daugh- 

 ter chromosomes or diasters, together with one polar body and a part 

 of the achromatic spindle (Fig. 30, 6). Now a new nucleus is formed 

 about the daughter chromosomes which gradually assume the characters 



1 1t is believed that every species has a fixed and characteristic number of chromo- 

 somes in the dividing cells, and that in forms arising by sexual reproduction this num- 

 ber is even. In man the number is believed by some to be 16. by others 32. 



