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THE AMERICAN NATURALIST [Vol. LI 



make up a reaction system the elements of which bear a 

 more or less specific relationship to one another. It is 

 this specific interrelation of the factors of the reaction 

 system which determines that wheat produces wheat, and 

 corn, corn, and so on through the whole realm of living 

 matter. With this in mind it is at once apparent that 

 normal Mendelian behavior can not be considered as a 

 contrast of different reaction systems, but that in such 

 cases the two organisms contrasted must possess funda- 

 mentally the same reaction systems, only a relatively few 

 elements within the reaction system differing, and these 

 not in a fundamental fashion. In fact it seems entirely 

 logical in the light of modem Mendelian developments to 

 consider each particular locus as made up of a definite 

 nucleus, some complex organic compound perhaps, with 

 a number of end chains which may be altered in various 

 ways without changing the structure of the nucleus of the 

 locus. According to this conception the fundamental rela- 

 tion of the locus to the other elements of the reaction sys- 

 tem would remain unchanged, while the end product would 

 be altered in some particular manner. There is probably 

 no more striking confirmation of this conception than the 

 suggestive hypothesis of multiple allelomorphs which 

 Morgan and his associates (1915, I. c.) have developed. 

 Their results and those of others in this connection seem 

 to show clearly that the explanation of Mendelian differ- 

 ences on the basis of such a profound change as the drop- 

 ping out of an element from a delicately balanced reaction 

 system is practically out of the question. In multiple alle- 

 lomorphs we have not one, but several, changes within the 

 same locus. The similar effect which these changes have 

 on certain organs of the body, for example, that relation 

 shown in the locus W in Drosophila as a consequence of 

 which the normal red eye color may be changed to white, 

 eosin, or cherry depending upon a particular change in 

 the locus, are such as to indicate that these are probably 

 changes around the fringe of the molecule and not such 

 as fundamentally affect the structure of the entire locus. 

 Moreover, the relations thus exhibited again indicate 1 



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