12 



HISTOLOGY. 



chromosome are drawn apart as if by means of the outer spindle, or mantle 

 fibrils. In an unusual but important form of mitosis, known as hetero- 

 typical mitosis, the partially divided chromosomes remain for some time 

 united by their ends, in the form of rings. How such ring-shaped chromo- 

 somes may occur is shown in Fig. 12. Ordinarily the V's are completely 

 divided, and the separate halves travel, apex forward, toward their re- 

 spective poles. Two stellate groups are now observed and this stage is 

 called the dyaster (Fig. 13). Stretching between these groups are the 

 central fibrils of the spindle, not shown in the drawing. A development 

 of granules in these fibrils along the equatorial plane may take part in 

 forming a new transverse cell wall. 



The metaphase is the stage of division of the chromosomes, and by 

 some writers it is considered very brief, the monaster being counted the last 

 of the prophase, and the dyaster being included in the anaphase. 



FIG. 13. LATE METAPHASE: 

 DYASTER. 



FIG. 14. ANAPHASE: Di- 

 SPIREME. 



Anaphase. The chromosomes of either portion of the dyaster are the 

 same in number as those of the nucleus from which they came. Each 

 group represents half of the chromatic material. These new chromosomes 

 unite with one another, each group forming a spireme. The mitotic 

 figure thus produced is the dispireme (Fig. 14). The centrosphere loses 

 its radiations, becoming reduced to a zone of archoplasm, and the centro- 

 some often divides to form a diplosome. A nuclear membrane forms, 

 beginning at a point opposite the centrosomes. The nucleoli reappear 

 as the chromatin thread returns to a network by sending out branches. 

 Thus two resting nuclei have formed. Meanwhile the protoplasm along 

 the equator constricts, and here, sometimes aided by the granules of the 

 central spindle, the new cell wall develops to complete the process of mitosis. 



Summary. The stages described have been successively the reticular 

 quiescent stage, the monospireme, monaster, dyaster, dispireme, and the 

 return to the reticular condition. These terms refer to the arrangement 



