156 ROBERT T. HANCE. 



There is also an increase in the size of the chromosomes as can be 

 seen by comparing Fig. i with Figs. 3 and 4. This is an actual 

 increase in size and may be caused by the increased or richer 

 nourishment that it is possible to offer cells reared in cultures 

 rather than by the mere flattening of the cell and its contents. It 

 seems apparent, although but few accurate measurements have 





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4, 



Photographs of dividing chick cells. X 1000. 



FIG. i. Late prophase of mitosis of cell growing in tissue culture. 

 FIG. 2. Prophase of mitosis of cell in tissue culture. Note the extreme flatness of 



the arrangement of the chromatic particles. 



FIGS. 3 AND 4. Polar views of metaphase plates found in sectioned chick embryos. 

 Compare their dimensions with Fig. i. 



been made, that whatever has caused the chromosomes to increase 

 in size has affected all equally. This observation is in harmony 

 with the results reported elsewhere (Hance, 17 and 18) where it 

 was demonstrated that an increase in the total amount of 

 chromatin in a given cell was the result of a proportional increase 

 in the size of each individual chromosome. 



The prophase stages of division which under ordinary con- 

 ditions are like a ball of threads are in the cultures spread out so 

 flatly that every granule of chromatin in the nucleus can fre- 

 quently be recorded by photomicrograph as readily as can be 

 the chromosomes of a very flat metaphase plate (Fig. 2). As the 

 cells in the cultures are so exceedingly thin division never takes 

 place perpendicular to the cover-glass but by the time mitosis 

 has reached metaphase the chromosomes rearrange themselves 

 so that division occurs in the plane of the cover. Consequently 

 polar views of the metaphase cannot be found in cells in cultures 

 although the very late prophase is so similar that for purposes 



