CELLS IN DIVISION 



could probably be used for this purpose. It is unlikely that movement 

 of water is never involved in nuclear reconstruction, for Shigenaga^^ 

 has directly observed the inhibition of the process when water was 

 withdrawn from a staminal hair cell of Tradescantia by adding a hyper- 

 tonic medium. It does not seem that an exactly comparable experiment 

 on animal cells in mitosis has ever been done, although several authors 

 have shown that the course of cell division can be gravely disturbed by 

 hypertony. In grasshopper spermatocytes, the spindle is much more 

 sensitive to such treatment than are the chromosomes (Belar^^). 



M/fof/c stage 



ffesfing 



Prophase 



Promefaphase 



flefaphose 



Anaphase 



Te/ephase max. 

 confr. 



Other 



Peconstrucfion 



Resting 



Cut ear 

 diploid 



300 500 700 900 1,100 1,300 1,500 1,100 

 Ai/eroge volume of figure in cubic microns 



Figure 26 Volume of nuclei and mitotic figures in various 



mouse tissues. From Biesele et alii (By courtesy, University of Texas 



Publications).^^ 



AiSENBERG^^ examined the dividing cells in the web of a frog's foot 

 which was immersed in Ringer Solutions of varying osmotic pressure 

 and made counts of each phase of mitosis therein. It does not appear 

 from his figures that the proportion of telophases was increased in 

 hypertonic media. There is no indication in Gray's^^ careful study of 

 cleavage of the sea-urchin egg in sea water to which various amounts 

 of sodium chloride had been added, that nuclear reconstruction was 

 specially sensitive to this treatment. However, it is possible that in 

 animal cells, the effect of variations in the osmotic pressure of the 

 external medium is not transmitted to the nucleus because of changes 

 in the water content of the cytoplasm at that time, for its behaviour 

 often suggests that water movements are then in progress. In Acan- 

 thamoeba for instance, Comandon and de Fonbrune^* have observed 



