546 CLAKENCE E. McCLUNG 



my belief in the necessity for this definiteness in the grasshoppers. 

 We do not yet know how much difference there may be in the organi- 

 zation of the various chromosomes of a complex nor how variable in 

 importance they may be. 



A more carefu] reading of my papers would have saved some 

 of my critics much futile argument. 



While I have thus avoided any consideration of the general 

 topic of chromosome variations in other papers, I should like 

 now to examine some of the data relating to this subject. It is 

 important that this be done, because most of the attacks upon 

 the theory of chromosome individuality have proceeded from 

 investigators who either found, or think they found, variations 

 in chromosome numbers wdthin individuals or species. Such 

 attacks have run the gamut, from assertions that chromosomes are 

 merely physical aggi^egates without morphological value, down to 

 questions regarding the definition of the term chromosome. In 

 undertaking such a general discussion I shall base my opinion 

 largely upon material with which I have personal familiarity. 

 Much harm has come from attempts to homologize results from 

 wddely different materials by persons w^ho have no first hand ac- 

 quaintance wdth the conditions discussed. With our present 

 knowledge of cellular phenomena as slight as it is, such lengthy 

 critiques, involving the interpretation of other investigators' 

 interpretations, can accomplish little good and may greatly 

 retard progress by fixing attention upon relatively unimportant 

 details. A striking instance of this has been the controversy 

 regarding pre- or post-reduction, extended long past the time 

 when it was definitely know^n that the question of the segrega- 

 tion division is one of the individual chromosome and not of 

 a whole mitosis. The matter of chromosome organization is, 

 however, fundamental to all om' present conceptions of the cell 

 in relation to the larger problems of biology, and the evidence is 

 cumulative that the essential assumptions of our hypotheses 

 are justified. On the other hand it seems clear that the natm-e 

 of chromosome integration varies with different groups and that, 

 for this reason, we must be cautious in carrying over the con- 

 clusions reached from a study of one population of organisms to 



