THE DETERMINATION OF SEX 589 



of the facts of parthenogenesis, without postulating specifically 

 different male and female " determiners " ; and it avoids the 

 necessity for assuming selective fertilisation, which is such a 

 stumbling-block in the way of the qualitative interpretation. 

 Further, the quantitative view, as thus stated, can readily be 

 applied to cases like that of Mctapodius, where the total 

 chromatin-mass varies in the same species, independently of 

 sex, 1 or of Nezara and Oncopeltus, where the total chromatin- 

 mass is the same in both sexes. Here we perceive the possi- 

 bility of extending the interpretation over a much larger 

 series of forms than those in which a dimorphism of the 

 spermatozoa or eggs is visible to the eye. It may be urged 

 against this that visible sexual differences in the chromosomes 

 are exceptional (which is probably the fact) and that we have 

 no right to transfer the conclusions based on these excep- 

 tional cases to the more usual ones in which such differences 

 (apparently) do not exist. There are at least two replies to 

 this. One is the fact, already mentioned, that all gradations 

 have been found between species which do, and species which 

 do not, show such differences. Another is that experiment 

 demonstrates a quite analogous sexual predestination in germ- 

 cells where observation has not thus far demonstrated any 

 visible differences, in the chromosomes or otherwise. It will, 

 I think, be found difficult to escape the conclusion that the same 

 principle applies to all these cases ; though such a conclusion 

 must of course be held subject to revision. 



In attempting a broader development of the foregoing view 

 we at once become aware that the particular formulas thus far 

 employed — XX = Female and X (or XY) = Male — cannot hold 

 true of all forms. It obviously does not apply to cases where 

 females as well as males are produced from germ-cells that 

 develop with the haploid number of chromosomes, e.g., the 

 spores of dioecious plants such as mosses and liverworts. It 

 will not, apparently, apply to the case of the sea-urchin ; and, 

 as Castle has shown, 2 it seems inadmissible in case of the 

 remarkable results of crosses between Abraxas grossulariata 

 and A. lacticolor, as worked out by Doncaster and Raynor. 

 In all cases, indeed, where the female is the heterozygous or 

 heterogametic sex, this formulation seems to be excluded. It 

 nevertheless remains possible, as I earlier suggested in the case 

 1 Wilson, Journ. Exp. Zool. 1909, vi. s Science, March 5, 1909. 



