NUCLEAR AND CELL-DIVISION. 



6 9 



late figures are developed about the respective poles of the central 

 spindle. The appearance presented is known as a diaster. Our 

 knowledge of the part taken by the amphiaster or achromatic 

 spindle in metakinesis is not above controversy. It would appear, 

 however, that certain cytoplastic fibers, which arise from the cen- 

 trosphere and hang over the central spindle and chromosomes, 

 designated as mantle fibers, assist in drawing the daughter chromo- 

 somes toward the poles of the central spindle. 



(c] Anaphases. After the formation of the diaster, the loops be- 

 longing to each stellate figure are joined together to form a skein, 

 thus forming the dispirem. The chromatin threads of the two 

 skeins gradually assume the disposition found in the resting nucleus. 

 This process takes place in such a way that the threads of the 



Dispirem. 



Diaster. 



Diaster. 



Monaster. 



Resting nucleus. 

 Metakinesis. 



Diaster. 



- Daughter cells. 



Spirem. 

 Fig. 30. Mitotic division of cells in testis of salamander (Benda and Guenther). 



skeins (or the single thread) send out lateral processes. These 

 interlace, and little by little reproduce the network of the resting 

 nucleus ; at the same time the nuclear membrane and the nucleolus 

 reappear. In this stage the changes that lead to the division of the 

 cell-body are observed. In some cases the division of the cell-body 

 is ushered in by an equatorial differentiation of the connecting 

 threads of the central spindle. Chains of granules, arranged in 

 double rows, are seen to appear in this region. The cell now begins 

 to contract at its equator, the contraction extending between the 

 two chains of granules until the cell is completely divided. At 

 this time, also, the threads of the amphiaster disappear or are drawn 

 into the nucleus. The centrosomes, with centrospheres, again lie 

 by the side of the daughter nuclei. 



