32 MODES OF RESEARCH IN GENETICS 



objective data are the statistical results of Mende- 

 lian experiments. But, and herein seems to me to 

 lie the logical as well as the factual superiority of 

 Morgan's view over that of Bateson and Punnett, 

 pains have been taken at every step to check the 

 hypothesis by direct cytological observation as 

 well as experimental evidence. The net result 

 is that, up to the present time, everything that is 

 known about the cytology of the germ cells in 

 Drosophila is in entire and complete accord with 

 Morgan's interpretation of the experimental results. 

 The manifoldness and complexity of these experi- 

 mental results have now become so great as to 

 make it extremely improbable that this agree- 

 ment between cytological and experimental data 

 is fortuitous. On the contrary, the evidence 

 comes extremely close to a logically complete ex- 

 perimental demonstration of two points ; namely, 

 (1) that the factors which have a differential 

 effect in the determination of inherited characters 

 are contained in the chromosomes, and (2) that 

 the factors have a linear arrangement in these 

 bodies. 



The extraordinary difficulty of adducing any- 

 thing like complete proof for the location of 

 hereditary determiners in morphologically definite 

 elements of the cell organization must be obvious 

 to any one. The evidence is bound to be largely 

 of an inferential character. On that basis the 

 weight of evidence now available strongly indi- 



