DETERMINATION OF SEX DONCASTER. 483 



and the females heterozygous in respect of a character so intimately 

 related with sex, it strongly supports the idea that the same may be 

 the case with the sex determinants themselves. 



If this instance stood alone it might seem rash to found on it such 

 a far-reaching theory of the nature of sex. But exactly similar 

 cases have been found elsewhere. Miss Durham x has described 

 almost identical phenomena in the case of canaries of the Cinnamon 

 variety, which have pink eyes. A pink-eyed hen paired with a black- 

 eyed cock gives offspring which are all black-eyed ; but a black-eyed 

 hen by a pink-eyed cock gives males which are all black-eyed, and 

 pink-eyed females, together with sometimes a small proportion of 

 black-eyed females. This occurrence of exceptions suggests some dis- 

 turbing factor not present in the moths. Bateson, 2 and Pearl and 

 Surface, 3 have discovered similar cases in fowls, and Correns from 

 experiments on plants (Bryonia) has come to a similar conclusion, 4 

 except that he regards the male as heterozygous and the female 

 homozygous. 



Confirmatory evidence may be drawn from other observations. 

 One of these is the effects of castration. In vertebrates castration of 

 the male may prevent the appearance of the male secondary sexual 

 characters but does not cause the appearance of characters proper 

 to the female. Removal or atrophy of the ovary, however, may bring 

 about the development of characters normal in the male. In the 

 Crustacea the opposite result is found. 5 A female whose ovaries are 

 destroyed by a parasite has its secondary sexual characters reduced; 

 a male assumes more or less completely the characters of the female. 

 And if the parasite dies and the host recovers, the ovary of the 

 female may again become functional; but in the male under such 

 circumstances eggs may be produced in the testis. Geoffrey Smith 

 concludes from these observations and from others on the Cirripedes 

 that the female is homozygous in sex and the male heterozygous. 

 There seems no a priori reason why this should not be true in the 

 case of the Crustacea and flowering plants, while the converse is the 

 case in moths and vertebrates. 6 



1 Reports to Roy. Soc. Evolution Committee, vol. 4, 1908, p. 57. 



2 See note in Science, vol. 27, 1908, p. 785, referred to above. For full account of 

 this case, and discussion of the whole subject, see Bateson, Mendel's Principles of 

 Heredity (Camb. Univ. Press, 1909), Chap. X. 



" Pearl and Surface, Ann. Rept. Maine Agric. Exper. Station, 1910, pp. 84-116. 

 4 Bestimmung und Vercrbung des Geschlechtes (Borntraeger), 1907. 



5 G. Smith, Naples Monograph, Rhizocephala, 190G. [Sec also Smith, 'Studies in the 

 experimental analysis of sex.' I-V, Quart. Journ. Micr. Sci., 1910-11.] 



6 [This was written before the publication of Morgan's important papers on Sex-limited 

 inheritance in Drosophila (Science, vol. 32, 1910, p. 120, and American Naturalist, vol. 

 45, p. 65, 1911). In this fly the inheritance of several characters shows phenomena the 

 exact converse of those found in Abraxas, indicating that the male is heterozygous for 

 the sex determiner, and transmits the characters concerned only to his female offspring. 

 This suggests either that in some cases, e. g., Abraxas and fowls, the female is heterozy- 

 gous and the male homozygous, in others, e. g., Drosophila, the male is heterozygous and 

 the female homozygous for sex determiners, oT that both sexes are heterozygous with 

 selective fertilization. For fuller discussion of this more recent VoYk the reader is 

 referred to the p'apers on the subject by Mbrgan, Wilson, Miss Stevens, the wl-iter, ete.] 



