296 



me to be primarily connected with the changes in activity which are 

 otherwise apparent in the increase in size of cytoplasm and nucleus 

 during the growth-period. 



The evidence from observations on amitosis possesses one advant- 

 age over that derived from the examination of chromosomes; the ab- 

 sence of visible chromosomes in amitosis is a fact of direct obser- 

 vation in all cases, while the idea of continuity or individuality is an 

 inference from observation of selected cases. 



In the light of the observed facts the hypothesis of "chromosome- 

 individuality" becomes very improbable as a universal hypothesis. It 

 is not impossible that in some cases chromosomes maintain their "indi- 

 viduality" for a limited period but there are at present no sound 

 reasons for going further than this. The problem of the significance 

 of the chromosome cannot be solved until we know something of the 

 nature of the processes involved in both mitosis and amitosis. Mean- 

 while the problem of the conditions determining the two forms of 

 division presents a most promising field for observation and experiment, 

 with the probability of a better knowledge of the nature of the 

 phenomena and the processes and conditions with which they are 

 associated. In this connection the exact determination of the stages 

 in which change from one form of division to the other occurs will 

 doubtless prove to be of value. I hope to present at another time 

 certain descriptive and experimental data bearing upon this problem. 



Hull Zoological Laboratory, University of Chicago, November 1906. 



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