454 THE AMERICAN NATURALIST [Vol. XLIV 



sumption that unit characters in heredity are preformed; 

 especially since those who assume such characters to be 

 the basis of heredity have as a class — with some excep- 

 tions, however — shown a strong predilection towards lo- 

 cating their indivisible units in the chromosomes. 



These and other conditions have combined to produce 

 two opposing views and the chromosomes have come to 

 be the chief bone of contention. I shall attempt, there- 

 fore, to limit my discussion to this topic, at the risk of 

 appearing to take rather a narrow point of view. 



We can trace to the important work of Boveri a great 

 deal in our modern conception of the idea of the chro- 

 mosomes in heredity and development. We owe to 

 Boveri the current conception of the individuality of the 

 chromosomes ; we owe to him the discovery of facts that 

 go to show in a sense the independence of the chromo- 

 somes of the cytoplasm in which they lie ; and most im- 

 portant of all we owe to him the idea that the chromo- 

 somes may be individually different and that development 

 depends on the presence in the cells of samples of each 

 kind of chromosome. Let us take up these points in turn. 



Individuality is a word with vague meanings. Boveri 

 has, however, denned very precisely the limited way in 

 which he applies this term to the chromosomes. Whether 

 we agree that the facts show the chromosomes to possess 

 this kind of individuality is a question to be further ex- 

 amined, but admitting differences of view possible 

 Boveri 's careful analysis of the situations must excite 

 our admiration and respect. Wilson's expression, the 

 genetic continuity of the chromosomes, seems, however, 

 to better express Boveri 's attitude than the word individ- 

 uality used by Boveri himself so far as the facts of direct 

 observation are concerned ; but if we extend this term to 

 include Boveri 's deductions from certain experimental 

 work, then the word individuality means something more 

 than genetic continuity. 



Applied to the chromosomes, individuality means that 

 the chromosome that passes into the resting nucleus 

 is substantially the same that comes out at the next 



