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TELOPHASE AND RECONSTRUCTION 289 



granules become arranged like the iron filings in the field 

 of a magnet. In support of the latter opinion is the fact 

 that the polar ends of the fibers do not seem to be at- 

 tached to anything solid enough to permit them to exert 

 a tractive force on the chromosomes. Moreover, the 

 polar ends often seem to dissolve away even before the 

 chromosomes have completed their movement. When 

 we consider that we do not yet understand at all well 

 how any sort of protoplasmic movement is produced, it 

 should not be surprising that this particular sort should 

 still be obscure. 



The Telophase and the Reconstruction of the 

 Nucleus (Figs. 68.4 and .5). — When the chromo- 

 somes arrive at their respective poles they at first 

 draw close together and often become so crowded 

 that it is difficult to distinguish their individual out- 

 lines (telophase). The next step ordinarily consists 

 in the appearance of a new nuclear membrane closely 

 surrounding the crowded chromosomes. Shortly it will 

 be seen that the membrane is enlarging and that there 

 is now a small amount of nuclear sap. It is the cur- 

 rent opinion that the membrane is merely a thin layer 

 of cytoplasm of a more solid character than the rest. In 

 fact a very similar layer is present on the outside, next 

 the cell-wall, if there is one, or forming the outer cover- 

 ing of one-celled animals. If one punctures the outer 

 layer of protoplasm with a fine needle the more fluid part 

 at once runs out through the hole, but as soon as it comes 

 in contact with the surrounding water it immediately 

 forms a new membrane. It is supposed that the cyto- 

 plasm reacts in this same way to the nuclear sap as soon 

 as it is formed, and thus gives rise to the nuclear 

 membrane. 



Individuality of the Chromosomes. — As the nucleus 

 expands, the rod-like chromosomes also begin to expand 

 and to become distended by vacuoles, possibly of nuclear 

 sap. This process might be roughly likened to the holes 



