538 THE AMERICAN NATURALIST [Vol. XL VIII 



series separately, and I shall therefore use only two terms 

 in speaking of gametic ratios. By adding together the two 

 halves of the series larger numbers are obtained, so that 

 chance deviations are relatively smaller. Differential 

 viability is also partially overcome in this way. Of 

 course on the reduplication theory both terms of the 

 gametic ratio must be integers, since they represent num- 

 bers of cells, but nevertheless it has seemed to me more 

 convenient for purposes of calculation to express them 

 always in the form n : 1. Thus a gametic ration of 3 : 2 

 may be written 1.5 : 1. 



It was suggested by Bateson and Punnett ('11) that 

 the intensity of coupling and of repulsion between the 

 same two pairs of genes may be identical. That this is 

 substantially the case has been shown again and again in 

 Drosuphila, and has become a truism among those work- 

 ing on that form. Before presenting data on this point I 

 wish to bring up another matter on which the same data 

 have a bearing. Punnett ( '13) has said, ' ' But where three 

 [pairs of] factors are concerned . . . the value of the 

 primary reduplications is evidently altered, and there 

 would seem to be some process whereby these reduplica- 

 tions react on one another." Bailey ('14) has suggested 

 that the nature of this interaction may be such as to cause 

 the two primary series to be of equal intensity. It may be 

 categorically stated that there is no interaction effect in 

 Drosophila. The best data for a test of the relative inten- 

 sity of coupling and repulsion, and of "fundamental," 

 "primary" and "secondary" reduplication series, in- 

 volving the same allelomorphic groups, is that furnished 

 by the relations of the various forms of IF {W, w, w e , tv c ) 

 to the M pair of allelomorphs (M and m). Table I is a 

 summary of the data on this case. In computing the 

 fundamental series I have used only the data from such 

 of my own experiments as involve only two pairs of genes, 

 since that from other sources is for the most part made up 

 of primary series in which the other primary series in- 

 volved is masked. 



