A CRITICAL EXAMINATION 25 



tion of the egg. The broad general result of the 

 investigation of this problem is that certain defi- 

 nite nuclear components, the chromosomes, are 

 distributed during gamete formation in a manner 

 which parallels the distribution of hereditary 

 characters as observed in Mendelian segregation. 

 In other words, the chromosomes behave in game- 

 togenesis as any structures which were the bearers 

 of the causative agents of the inherited characters 

 would be expected a priori to behave. This dis- 

 covery is clearly one of first-class importance. 

 It is justly to be regarded as one of the greatest 

 achievements of modern biology. It furnishes 

 strong grounds in favor of the basic conclusion 

 that the determination of hereditary specificity 

 is resident in the chromosomes. The familiar 

 and widely accepted doctrine that the chromo- 

 somes are the exclusive "bearers" of hereditary 

 qualities is a crude form of this conclusion. 

 Those who have defended this doctrine, however, 

 have been compelled from time to time to qualify 

 their statement of it, because of the discovery of 

 facts which either were absolutely difficult to 

 reconcile with it, or were relatively more easily 

 to be accounted for on some other hypothesis. 



The greatest methodological difficulty in the case 

 lies in the fact that cytology is essentially an 

 observational and not an experimental science, 

 though some brilliant beginnings in the latter 

 direction have been made, notably by Boveri. 



