38 RICHARD GOLDSCHMIDT. 



segmentation by a rudimentary division. No case of this kind 

 has been proved beyond doubt. 



The current ideas about the relation of parthenogenesis and 

 sex are primarily concerned with the chromosome number and 

 with an eventual extrusion of a single sex-chromosome. If these 

 conceptions are valid, the different methods of reaching the 

 diploid number of chromosomes would not affect the resulting 

 sex. But, at the same time, these conceptions have failed to 

 explain why parthenogenesis produces only males or only females 

 or both sexes, and that sometimes with, sometimes without, 

 reduction. The ideas about sex-determination which we have 

 developed during the last few years enable us, as we believe, 

 better to understand the different facts about parthenogenesis 

 and to fit them into the general scheme of sex-inheritance. 



Since we stated our views in a general way not long ago (Gold- 

 schmidt. 1916). we do not need to repeat them here in extenso. 

 We might mention only that we believe to have proved (i) that 

 there are different sex-factors for the sexes, both acting inde- 

 pendently in both sexes; (2) that both factors exhibit a definite 

 quantitative action ; (3) that the definitive sexdepends upon which 

 factor has the higher value, or, expressed in a formula, F - - M 

 > e = 9 , M - - F > e =<?', (4) that one of these factors is 

 carried in the sex-chromosome, the mechanism of their dis- 

 tribution or, in Mendelian symbolism, of the gamete-formation 

 in heterozygosis being the means of regulating the values for e 

 in favor of F or M respectively; (5) that the factor not carried in 

 the sex-chromosome, namely F in the case of female heterozy- 

 gosis, M in male heterozygosis, is inherited maternally, probably 

 in the protoplasm of the egg. 



Thus the conclusions which we must draw concerning the re- 

 lation of parthenogenesis and sex are of course different from 

 those of older writers. Let us first glance at the possible com- 

 binations to be derived from our conceptions. For convenience 

 we use the formulae: (FF) Mm = 9 ; (FF) MM = 6", in the 

 case of female heterozygosis, and (MM) Ff = <?, (MM) FF = 9 , 

 in the case of male heterozygosis. And we keep in mind the 

 fact that the factors within the brackets are inherited maternally 

 and are. therefore, contained in every egg, the others being carried 



