184 



THE CELL 



constituents absorb staining solutions, compared to that observed 

 in former stages. The more distinctly and sharply defined the 

 threads grow, the more strongly stained do they become, and the 

 more energetically do they retain the colouring matter, whereas 

 the network of the resting nucleus exhibits these properties to a 

 much less degree. This may be especially well demonstrated if 

 Graham's method of staining be employed, for whilst the resting 

 nuclei are completely decolourised, those that are preparing to 

 divide, or are actually undergoing the process, are so strongly 

 stained that they cannot fail to attract the attention of the 

 observer. 



During the first stage of coil formation the nucleoli are still 

 present ; however, they gradually diminish in size, until after a 

 short time no trace of them can be seen. Up till now it has not 

 been determined with certainty what is formed from them. 



Whilst the coil is developing, careful observation reveals a small 

 spot on the surface of the nucleus. This becomes more and more 

 distinctly defined as the process progresses : it has been designated 

 by Rabl the polar area (Fig. 77). The opposite surface of the 



nucleus is the anti-polar area. The 

 nuclein threads become gradually 

 more and more distinct, and ar- 

 range themselves so as to point 

 towards these two areas. 



Starting from the anti-polar 

 region they collect in the neigh- 

 bourhood of the polar area. " Here 

 they bend round upon themselves 

 in a loop-like fashion, and then 

 return, by means of several small, 

 irregular indented loops, to the 

 neighbourhood of their starting 

 point." Later on the threads be- 

 come shorter and correspondingly thicker; they are less twisted, 

 and cling less closely together, so that the whole skein looks much 

 looser. In the meantime their arrangement in loops gradually 

 grows more and more distinct. In favourable cases it has been 

 Lscertained that there are twenty-four such loops or nuclear 

 segments ; this number is constant for the tissue cells and sperm- 

 mother-cells of Salamandra and Triton. 



Meanwhile the two centrosomes and the SDindle most im- 



FIG. 77. Diagrammatic representa- 

 tion of a nucleus with a polar area, in 

 which the two centrosomes and the 

 spindle are developing. (After Flem- 

 ming, PI. 39, Fig. 37.) 



