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THE AMERICAN NATURALIST [Vol. XLVIII 



Thus we are forced to assume an enormously complex 

 series of cell divisions, many of them differential, pro- 

 ceeding with mathematical regularity and precision, but in 

 a manner for which direct observation furnishes no basis. 

 It seems to me that it is not desirable to assume such 

 a complex series Of events unless we have extremely 

 strong reasons for doing so. I can see no sound reason 

 for adopting the reduplication hypothesis. It apparently 

 rests on two discredited hypotheses: somatic segregation, 

 and the occurrence of members of the 3 : 1, 7 : 1, 15 : 1, etc., 

 series of gametic ratios in more cases than would be ex- 

 pected from a chance distribution. 



The chief advantage of the chromosome hypothesis of 

 linkage which has been proposed by Morgan ('11), and 

 which I have followed elsewhere, seems to me to be its 

 simplicity. In addition it appeals to a known mechanism, 

 and a mechanism toward which the experiments of Boveri, 

 Herbst, Baltzer and others point as the correct one. It 

 explains everything that any of the forms of the redupli- 

 cation hypothesis does, and in addition offers a simple 

 mechanical explanation of the fact that "secondary 

 series" are always smaller than T row's "'special hypoth- 

 esis" calls for them to be. On the reduplication hypoth- 

 esis this fact must merely be accepted, for, I think, it 

 can not be explained. 



LITERATURE CITED 



Bailey, P. G. 



'14. Primary and Secondary Reduplication Series. Jour. Genet., HI. 

 Bateson, W., and R. C. Punnett. 



Jour. Genet., I. 8 P 



Bridges, C. B., and A. H. Sturtevant. 



'14. A New Gene in the Second Chromosome of Drosophila, etc. Biol. 



Bull, XXVI. 

 Gregory, R. P. 



Boyal Soc., 84. ^B. g P T 



Morgan, T. H. 



'10. Sex Limited Inheritance in Drosophila. Science, XXXIL 



