188 



THE CELL 



more closely together, so that it becomes very difficult to count 

 them and to trace their further development ; in fact, it can only 

 be accomplished in exceptional cases. 



Fourth Stage of Division. 



During this stage each group of daughter-segments becomes 

 gradually re-transformed into a vesicular resting nucleus (Fig. 81). 

 The threads draw still more closely to- 

 gether, become more bent and thicker ; 

 their surfaces grow rough and jagged, and 

 small processes become developed exter- 

 nally upon them, whilst a delicate nuclear 

 membrane develops around the whole 

 group. The radiated appearance around 

 the centrosomes gradually grows less and 

 less distinct, until it soon quite disappears. 

 Finally, also, the centrosomes and the 

 spindle fibrils can no longer be distin- 

 guished. It has not yet been decided what 

 they develop into. In fact, their origin and 

 their disappearance are equally shrouded 

 in mystery. Near to the place where the 

 centrosome was situated a depression may 

 be seen in the newly forming daughter 

 nucleus. Rabl considers it to be the above- 

 described polar area of the nucleus which 

 is seen preparatory to division, and is of opinion that the centro- 

 some has ensconced itself within it, being enclosed in the proto- 

 plasm of the cell-body. The nucleus gradually swells up more 

 and more through the absorption of nuclear sap, and becomes 

 globular in form, whilst the framework of the resting nucleus, 

 with its irregularly distributed nuclein granules of various sizes, 

 is reconstructed. Further, one or more nucleoli have made their 

 appearance in the framework during the process of reconstruction, 

 but as yet no one has succeeded in discovering their origin. 



When, at the commencement of the fourth stage, the two 

 daughter-stars are separated as far as possible from one another, 

 and have taken the preliminary steps towards becoming trans- 

 formed into the resting daughter nuclei, the cell-body itself begins 

 to divide. The radiations at the centrosomes have now at- 

 tained their greatest size. At this period a small furrow becomes 



FIG. 81. Diagrammatic 

 representation, of nuclear 

 segmentation (after Flem- 

 ming). The resting nucleus 

 has commenced to build it- 

 self up out of the daughter- 

 segments. (From Hat- 

 schek.) 



