CH. II.] 



CELL DIVISION 



17 



studied. The following figure (fig. 18) shows some of the typical 

 stages of karyokinesis as observed by Klein : 



FIG. 18. Karyokinesis. A, ordinary nucleus of a columnar epithelial cell ; B, c, the same nucleus in 

 the stage of convolution; D, the wreath or rosette form ; E, the aster, or single star; F, a nuclear 

 spindle from the Descemet's endothelium of the frog's cornea ; o, H, i, diaster ; K, two daughter 

 nuclei. (Klein.) 



The process may be divided into the following stages : 

 1. The non-dividing nucleus (fig. 19.) 



Node of network 



Node of network 



---*- Nuclear membrane. 

 Nucleolus. 



1 Nuclear matrix. 



Nuclear network. 



FIG. 19. The resting nucleus. (Waldeyer.) 



2. The spirem or skein stage : the nucleoli dissolve, the secondary 

 fibres disappear, and the primary loops running from polar to anti- 

 polar regions remain (figs. 8, 20). In 



some cells there is at first one long, 

 much twisted thread, which subse- 

 quently breaks up into segments. The 

 loops are called chromosomes. 



3. Each loop becomes less convo- 

 luted and splits longitudinally into two 

 sister threads, and the achromatic 

 spindle appears (fig. 21, A and B). 



4. The equatorial stage; monaster. 

 The nucleus has now two poles, those 



of the spindle ; and at each pole there is a polar corpuscle or centro- 



B 



FIG. 20. Early condition of the skein 

 stage viewed at the polar end. I. c./., 

 looped chromatic filament, i./., irre- 

 gular filament. (Rabl.) 



