A Modification of the Sex Ratio, and of other Ratios, etc. 245 



on page 326 throws light on this question. In the Fj gametes there 

 are two kinds of eggs differing by the presence of large R and small 

 r; both are absent in the male producing sperm. The expectation is 

 for equality of long males and miniature males if we ignore the ele- 

 ment of repugnance. If we reckon half of the long winged flies (785) 

 as males, there are 396 long males to 397 miniature males. There 

 is no repugnance, therefore, in the case of the factor R. It is impro- 

 bable, therefore, in the cases given above (for the other factor M) in 

 some of which R was unequally distributed, that R makes any 

 difference. 



The experiments have led to the detection of two important 

 conditions affecting the Mendelian ratios, viz.: one which for brevity 

 I have called the element of prematuration and one the element of 

 repugnance. In earlier papers both came under the head of "viability". 

 The term has now been relieved of two incumbrances, but may be 

 conveniently used for other remaining imknown elements that affect 

 the ratios of adult individuals. 



July ID* 1912. 



