Inheritance Materials of Germ-Cells 85 



ent to offspring; the apparent equality (it should never be 

 forgotten that the dogma of equality does not rest on rigor- 

 ous quantitative investigation) of the chromosomes in the 

 male and female germ-cells ; and the assumption that in 

 the male germ-cells the chromosomes alone are concerned 

 in fertilization. Even if these groups of assumed fact were 

 established with absolute certainty they would fah 1 far short 

 of being direct and final proof that chromatin is the only 

 hereditary substance. That this is true must be apparent 

 to all well-informed, carefully thinking biologists. The 

 most important grounds for this inconclusiveness are in- 

 volved in the facts and arguments set forth in the preced- 

 ing pages, but they may be summarized here, and in addi- 

 tion two other grounds may be pointed out. 



First and foremost, in my opinion, is the general truth 

 that chromosomes or even chromatic substance can not pos- 

 sibly be recognized as the sole bearers of hereditary sub- 

 stance, because the evidence is enormous in quantity and 

 direct and indisputable in quality that other substances par- 

 ticipate actively in the production of hereditary attributes. 

 There is no way of escaping this conclusion except by nar- 

 rowing the definition of heredity for the very purpose of 

 bringing it within the scope of the chromosome theory of 

 hereditary substance. The scope and fundamentality of 

 this aspect of the problem is sufficiently dwelt upon, we 

 may hope, in what has gone before. 



The two additional grounds for skepticism as to the con- 

 clusiveness of the cytological evidence will now be pointed 

 out. First, as to the evidence from the individuality and 

 continuity of the chromosomes. All that any careful 

 thinker claims or can claim for this evidence is that the 

 individuality and continuity of chromosomes as observed 

 are what might be expected if they were the germinal de- 

 pository of the organism's hereditary attributes. And the 

 question is constantly and naturally afeked, what other 



