THE CELL. 



39 



The phases of karyokinesis that follow metakinesis are similar to 

 those that preceded it, but occur in inverse order. 



4. The Diaster Phase (Fig. 13). — The chromosomes, having 

 reached the attraction-spheres, group themselves around the polar 

 body to form a wreath on a plane perpendicular to the axis joining 

 the poles. These wreaths, with the achromatic spindle, have an 

 appearance somewhat resembling the letter H, with a long cross- 



Fig. 15. 



Fro. 16. 



<^£'s Y .' ' ■, '•' .V-' 



Karyokinetic figures in epithelial cells. From a carcinoma removed by operation. (Lustig 



and Galleotti.) 



Fig. 15.— The centrosome has divided, but the nucleus is still in the resting condition. 

 Five nucleoli are represented within the nucleus. 



Fig. 16.— Metakinesis. The polar bodies have divided. 



piece, formed by the spindle, remaining uncolored or only faintly 

 tinged by nuclear dyes, while the uprights, made up of the chromo- 

 somes, are deeply stained. 



The ends of the chromosomes now unite to form a thread, and 

 the wreath-like arrangement gradually passes into that of the 

 dispirem. 



5. Dispirem (Figs. 14 and 17). — The halves of the original chro- 

 moplasm of the nucleus are now arranged in two skeins about the 

 poles. From these the two daughter-nuclei of the future cells are 

 formed (Fig. 18). 



During metakinesis the cytoplasm of the cell begins to show 

 signs of division. This may be accomplished through a constric- 

 tion of the body of the cell, which gradually becomes deeper and 

 finally severs the two portions ; or a series of punctiform or short 

 linear enlargements of the lines of the achromatic spindle appear 

 in its equator, and through these a plane of cleavage, dividing the 

 two new cells from each other, is finally established. 



It is rarely that any biological process assumes such mathemat- 

 ical precision as is displayed in karyokinesis. The purpose of that 



