486 Mr. L. Doncaster. [Jan. 25, 
producing ¢-bearing and ©-bearing spermatozoa (the latter being those 
without sex-determinant). Selective fertilisation was now supposed to 
occur, ¢-bearing eggs being fertilised by @-bearing spermatozoa giving 
females (2 ¢), g-bearing eggs by ©-bearing spermatozoa giving males 
(3 ©). 
It was pointed out that while such cases as Abraxas grossulariata, the 
cinnamon canary, and several breeds of fowls prove that the female is 
heterozygous in respect of sex, it is also clear that in some cases the male 
is in some sense heterozygous, as is proved by the inheritance of colour- 
blindness and other affections in Man. Since this was written, a new and 
remarkable case has been described by Morgan in Drosophila,* in which the 
heterozygous condition of the male is proved in exactly the same way as 
that of the female is shown in Abraxas. Now itis known from the work of 
Miss Stevenst that the male of. Drosophila has a pair of unequal idio- 
chromosomes, and thus produces two kinds of spermatozoa, and a recent 
paper by Guyert shows that in Man also two kinds of spermatozoa are 
formed. It appears, therefore, that in both the best-established cases in 
which the heterozygous condition as regards sex of the male has been shown 
by experiment and observation in heredity, the male is also heterozygous in 
respect of chromosomes, and produces two visibly different kinds of 
spermatozoa. In Abraxas, no such difference in the chromosomes of the 
spermatozoa is to be found,§ nor has it been found by Miss Stevens or 
Miss Cook in other Lepidoptera.|| These facts naturally suggest that in some 
species the male is heterozygous as regards sex, in others the female, and 
tend to support the suggestion of Wilson,{| Castle,** and Morgan,{f that 
specific male and female sex-determiners do not exist, but that femaleness 
consists in the presence of some extra factor superposed on what would 
otherwise produce maleness. If the female receives this factor from both 
parents, the male from only one, the female would appear homozygous as 
regards sex, the male heterozygous; if the female receives it from one 
parent and the male lacks it altogether, the female is heterozygous and the 
* ‘Science,’ July, 1910, vol. 32, p. 120. 
t ‘Journ. Exp. Zool.,’ vol. 5, p. 365. 
t ‘ Biological Bulletin,’ 1910, vol. 19, p. 219. 
§ Doncaster, ‘Proc. Camb. Phil. Soc.,’ vol. 16, pt. 1, p. 44. 
|| N. M. Stevens, ‘Carnegie Inst., Washington, Publ.,’ 1906, 36, Part 2, p. 48 ; Cook, 
‘Proc. Acad. Nat. Sci., Philad.,’ 1910; summarised, ‘Zentralbl. f. Allg. u. Exp. Biol.,’ 
1910, p. 620. 
“I ‘Science, January, 1909, vol. 29, p. 53. 
** ‘Science,’ March, 1909, vol. 29, p. 395. 
+t ‘Journ. Exp. Zool.’ 1909, vol. 7, p. 332. See also ‘Amer. Naturalist,’ vol. 45, 
No. 5380, p. 65, which has appeared since the above was written. 
