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THE AMERICAN NATURALIST [Vol. XLIX 



eases present to the genotype theory the following dilemma. 

 Either one gene is concerned in the case or many genes. If one 

 only is concerned, it is variable. If many genes are concerned, 

 they are so numerous (whether or not constant) that they present 

 to the observer of the visible character affected a continuous 

 variation series, one capable of indefinite displacement up or 

 down the quantitative scale. The supposed distinction between 

 continuous and discontinuous variation then vanishes. Selec- 

 tion in that case meets with no " fixed limit " beyond which it 

 cannot go. 



Mr. Muller is seriously disturbed (p. 573) because we are will- 

 ing to consider it possible that the " factor for hooded " may be 

 contaminated by " its allelomorph (the factor for self)" while 

 associated with it in the zygote represented by the F x rats. (The 

 evidence of modification is unmistakable, however one at- 

 tempts to explain it.) He says this is " violating one of the most 

 fundamental principles of genetics— the 'non-mixing of factors— 

 in order to support a violation of another fundamental prin- 

 ciple—the constancy of factors." Now, when, I should like to 

 inquire, did these principles become " fundamental "; by whom 

 were they established and on what evidence do they rest? I 

 should suppose that Bateson, president of the British Association, 

 might be considered fairly well posted on the " principles of 

 genetics," but neither in his earliest papers nor in his latest do 

 we find any mention of these sacred principles. In his recent 

 presidential address 4 he frankly states his belief that segregation 

 is often imperfect and that " fractionation " of factors fre- 

 quently occurs as a result of crossing. 



We shall look in vain, I think, for those " principles " outside 

 of the "Exakten Erblichkeitslehre" (or its imitations), and when 

 we inquire as to the experimental basis of the principles in ques- 

 tion we are met with the satisfied reply, ' ' Johannsen 's beans." 

 What a slender basis and what and absurd one from which to 

 derive the " fundamental principle " that Mendelian factors are 

 constant ! Yet to date this case, which admittedly involves no 

 clear Mendelian factor, is the only evidence worth mentioning in 

 favor of the constancy of Mendelian factors! Do biologists take 

 themselves seriously when they reason thus? Certainly no one 

 else will long take them seriously. 

 Finally, I may be permitted to correct two misapprehensions 

 * Science, August 28, 1914. 



