STUDIES ON CHROMOSOMES 423 



two members of each pair, and followed by a longitudinal split. 

 It would, no doubt, be premature definitely to accept this conclu- 

 sion at present; but it seems worthy of more attentive considera- 

 tion than it has yet received. 



Turning to the more general aspects of these problems, in what 

 sense may we be justified in speaking of the chromosomes as 

 bearers of the 'determiners' or factors of determination? I have 

 recently outlined in another place (Wilson, '12) my position in 

 regard to this question, and will here only indicate its most essen- 

 tial features. The 'determiners' or 'factors' on which unit-char- 

 acters depend need not be regarded as independent, self-propa- 

 gating germs (pangens, biophores, or the like) ; it is sufficient for 

 our purpose to think of them in a more vague way as only specific 

 chemicals entities of some kind. However they are conceived in 

 this regard, it would be a fundamental error to regard them as 

 'bearers' of the characters that depend upon their presence or 

 absence; for every character is produced as a reaction of the germ 

 considered as a whole or unit-system. Characters are 'borne' 

 (if the expression is permissible at all) by this system as a whole; 

 and the 'unit-factors' or 'determiners' postulated by students of 

 genetics need be considered only as specific, differential factors 

 of ontogenetic reaction in a complex organic system. Many 

 'unit-characters' are known to depend upon a number of such 

 unit-factors, in some cases probably upon a large number; and 

 they may be definitely altered this way or that by varying the 

 particular combinations of these factors. But any unit-factor 

 produces its characteristic effect only in so far as it forms a part 

 of a more general apparatus of ontogenetic reaction constituted 

 directly or indirectly by the organism as a whole. In all this, 

 a striking parallel exists between the physical basis of heredity and 

 the complex molecular groups of organic substances such as the 

 proteins. The relation of the ' determiners' to the qualities of the 

 organism considered as a whole may be compared to that which 

 exists between the protein 'Bausteine' and the qualities of the 

 protein molecular group as a whole. 



"Just as the qualities of a particular protein may be definitely altered 

 by the addition, subtraction or the substitution one for another of parti- 



