A Modification of the Sex Ratio, and of other Ratios, etc. 343 



long winged females to rudimentary males (see above (2)), are back- 

 crossed to rudimentary males there are produced many flies, both 

 males and females, in both classes, about foiu" long to one rudi- 

 mentary. Evidently under certain conditions there is little difficulty 

 in producing rudimentary males and females, while under other con- 

 ditions not a single one is produced yet the combination required 

 must be assumed to be the same in all cases. These anomalous 

 results may be explained in part by means of the following hypothesis. 



In the heterozygous female the egg has developed up to the time 

 of the extrusion of the polar bodies under the influence of M (i. e., 

 all the normal factors are present, at least in simplex). An egg 

 develops, therefore, with the same factors present that are present 

 in the egg of the wild fly. Not until the time of polar body for- 

 mation is the factor m lost from half of the eggs, i. e. from those 

 eggs that may produce rudimentary offspring. Hence the relatively 

 large number of eggs that may be fertilized by the rudimentary 

 winged male. 



On the other hand, in the rudimentary female the egg develops 

 without the presence of the factor M. If the absence of this factor, 

 in the prematuration development, makes the egg less fertilizable by 

 any sperm, the difference in the behavior of the two kinds of females 

 in question can be accounted for. In other words, a difference in 

 the origin of tlie egg may be connected with a difference in behavior. 



In the normal or wild male, M is present in simplex, but enters 

 only into the female producing sperm, although up to the time of 

 maturation the male producing sperm has (so to speak) been under 

 the same influence. But in the rudimentary winged males the sex- 

 cells lack M throughout their development. 



The recognition of this prematuration influence in the result gives 

 a measure of certain peculiarities (classified under the general term 

 viability) in the crosses. The measure of the prematuration influence 

 may be found by comparing the number of females produced when 

 a rudimentary winged male is paired to a wild female, with the 

 number of flies produced when a normal male fertilizes the same kind 

 of females. At present, I am not able to give the precise data, but 

 in general it may be said that many fewer females are produced in 

 the cross just given than are produced by wild flies. 



Other disturbances in the ratios cannot be explained as the results 

 of prematuration effects, but their cause may, however, be inferred 

 from an examination of the ratios themselves. 



