THE DETERMINATION OF SEX 587 



miners " are borne by different chromosomes or different 

 gametes ; and this remains true whether we assign these 

 "determiners " to the chromosomes or to something else. 



We are thus led, or rather driven, to seek a different 

 kind of interpretation. Could we regard the sexual dif- 

 ferentiation as due primarily to factors of a quantitative rather 

 than a qualitative nature, most of these difficulties would 

 disappear ; and such a conception would be in harmony 

 both with the cytological facts and with the experimental 

 evidence regarding sex-heredity. Several views of this general 

 type have in fact been suggested, some of them quite 

 independently of the facts here under consideration. For 

 example, Richard Hertwig advanced in 1905 * the view that 

 sex depends on the " Kernplasma-relation," or ratio of nuclear 

 to protoplasmic mass, the female being characterised by a 

 relatively smaller nuclear mass than the male. In support of 

 this view, Prof. Hertwig has contributed many interesting 

 experiments, and has suggestively discussed the facts in several 

 successive papers. Again, T. H. Morgan suggested in 1903 2 

 that the determinative factor in the bee may be quantitative, 

 the sex of the egg depending merely on whether the cleavage- 

 nucleus is made up of two germ-nuclei or one. The same 

 view appears in his Experimental Zoology (1907), where he also 

 suggests that the sperms containing the X-element produce 

 females simply because of " the greater amount of chromatin 

 brought into the egg by the sperm." This view approaches 

 one of my own suggestions, made in the preceding year, 3 but 

 differs from it in one very important respect. 4 



The conditions seen in such forms as Nezara, and the 

 remarkable facts observed in Metapodius, make one sceptical 

 of any hypothesis which postulates only a quantitative difference 

 of nuclear or chromatin mass taken as a whole. The case is 

 different if we limit the quantitative relation to a particular 

 kind of chromatin, namely, to that contained in the X-element. 

 Except for the fact that the Y-element is here left out of account 

 (for the reasons already stated), this is in all essentials identical 



1 Verh. Dentsch. Zool. Ges. 



3 Pop. Set. Monthly, December. 



3 Op. cit. 



4 An extended critique of the subject is given in Morgan's later work on 

 Phylloxera (1909) already cited. 



