28 Edmund B. Wilson 



selective fertilization are in large measure set aside. I therefore 

 think that the possibility of a Mendelian interpretation of sex- 

 production should be carefully examined, though as will be shown, 

 an alternative interpretation is possible. 



I. In such an examination the distinction between sex-deter- 

 mination and sex-inheritance should be clearly drawn; 1 for it is 

 well known that each sex may contain factors capable of pro- 

 ducing the characters of the opposite sex, and it may well be that 

 the patency or latency of the sexual characters is determined by 

 factors quite distinct from those concerned with their transmission 

 from parent to offspring. For the purpose of analysis it will, 

 however, be convenient to speak of the idiochromosomes or their 

 homologues as "sex-determinants," this term being understood 

 to mean that these chromosomes are the bearers of the male and 

 female qualities (or the factors essential to the production of these 

 qualities) respectively. They may also be designated (whenever 

 it is desirable to avoid circumlocution) as .sex-chromosomes or 

 "gonochromosomes." As a basis of discussion the Mendelian 

 interpretation may be taken to postulate, further, that the two 

 sex-chromosomes, which couple in synapsis and are subsequently 

 disjoined by the reducing division, are respectively male-determi- 

 nants and female-determinants in the sense just indicated. The 

 most convenient approach to the question is offered by the hetero- 

 tropic chromosome, since its unpaired condition in one sex renders 

 its mode of transmission more clearly obvious than that of the 

 idiochromosomes. The facts (especially as observed in Protenor) 

 clearly prove that this chromosome alternates between the sexes 

 in successive generations, passing from the male to the female in 

 the production of females, and from the female to the male in the 

 production of males (Fig. 6). The important bearing of this 

 on both sex-inheritance and sex-determination will appear beyond. 



Since the heterotropic chromosome is without a fellow in the 

 male it must, if it be a sex-determinant at all, be the male-determi- 

 nant, which exerts its effect uninfluenced by association with a 

 female-determinant. But since the spermatozoa that contain 



C/. Watase, '92. 



