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atford conclusive evidence in favor of the hypothesis since they are 

 not available for the demonstration of "individuality" during those 

 stages when the chromosomes themselves are not visible. 



Like certain other morphological hypotheses, the chromosome 

 hypothesis is concerned primarily with the significance of certain visible 

 phenomena, not with the nature of the processes involved. But it is 

 impossible to reach trustworthy conclusions regarding the significance 

 of visible phenomena without some knowledge of the underlying 

 processes. This constitutes to my mind a very grave objection to the 

 hypothesis and to the evidence thus far otfered in support of it. More 

 exact knowledge of the processes with which the visible phenomena 

 are associated may show that the latter are merely incidents or results 

 without significance except as indications of processes of certain 

 character. Substitution of the problem of significance of visible phe- 

 nomena for the problem of the nature of processes is always likely to 

 lead into blind paths. The real problem in connection with the chromo- 

 somes and mitosis seems to me to be the nature of the processes with 

 which the visible phenomena are associated. But problems of this 

 nature can be solved only by experimental methods. When we have 

 made further advance toward the solution of this problem we shall 

 be in better position to consider the significance of the visible phe- 

 nomena. 



Many of the observations which constitute important evidence in 

 favor of the hypothesis are of a nature requiring extreme caution and 

 must necessarily involve a large personal equation. It would be of 

 interest to know whether some of them, e. g. those concerning slight 

 but supposedly constant size-dift'erences, are not near the limit of the 

 probable error. But even if all of them are correct they are of the 

 nature of circumstantial evidence which is often most misleading when 

 most convincing. 



lu short, it is evident that the correctness of the hypothesis of 

 "chromosome-individuality" is very far from being demonstrated by 

 its supporters. The seemingly favorable character of most of the 

 evidence accumulated during the past few years is probably due to 

 the fact that cytologists have confined themselves almost exclusively 

 to the morphological features of certain stages in the life of the cell. 

 Most of our cytological methods, except those in the fields of neuro- 

 logy and haematology, have been developed with reference to the 

 mitotic figure. If the course of cytological investigation had been 

 different doubtless our cytological hypotheses would have been of dif- 

 ferent character. 



