CH. II.] 



KARYOKINESIS. 



nucleus ; the two attraction spheres become prominent in cell 

 division, and the connecting achromatic spindle is probably 

 also formed from them or from the achromatic material of the 

 nucleus. 



Fig. 20. Early condition of the skein stage viewed at the polar end. 

 chromatic filament, i. /., irregular filament. (Rubl.) 



Achromatic spindle 



I. e. /., looped 



Fig. 21. Later condition of the skein stage in karyokinesis. A. The thicker primary fibres 

 become less convoluted and the achromatic spindle appears, n. The thick fibres split 

 into two and the achromatic spindle becomes longitudinal. (Waldeyer.) 



Outer granular 

 zone. 



Split fibres. 

 Inner clear zone 

 Polar corpuscle. 



Fig. 22. Monaster stage of karyokinesis. (Waldeyer.) 



At this stage the nuclear membrane is lost, and thus cell 

 protoplasm and nuclear sap become continuous ; the protoplasm 

 immediately around the nucleus is clear; outside this is a granu- 

 lar zone, and here the granules are arranged radially from the 

 polar corpuscles. The star-like arrangement of these granules is 

 much better marked in embryonic cells, indeed the lines present 

 very much the appearance of fibrils (see fig. 23). 



The term amphiaster often given to this appearance must not 

 be confounded with the diaster to be immediately described. It 



