102 SCIENCE PROGRESS 



sometimes a small proportion of black-eyed females. This 

 occurrence of exceptions suggests some disturbing factor not 

 present in the moths. Bateson, 1 also, has discovered a similar 

 case in fowls, and Correns from experiments on plants {Bryonia) 

 has come to a similar conclusion, 2 except that he regards the 

 male as heterozygous and the female homozygous. 



Confirmatory evidence may be drawn from other observa- 

 tions. 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. 3 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. 



One of the points of difficulty about the theory that one 

 sex is homozygous and the other heterozygous in respect of 

 the sex-determinants is that it appears inconsistent with 

 Wilson's theory based on the study of " idiochromosomes." 

 But phenomena such as he describes have hardly been observed 

 outside most orders of Insects and possibly Arachnids, and are 

 probably not of universal occurrence. And if all individuals 

 of one sex are heterozygous, those of the other homozygous 

 in sex, it may be imagined that in the homozygous sex two 

 sex-determinants would not be necessary ; one of them might 

 become vestigial, as Wilson describes, if at the same time 

 spermatozoa bearing such a vestigial determinant can only 



1 See note in Science,vd\. xxvii. 1908, p. 785, referred to above. For full account 

 of this case, and discussion of the whole subject, see Bateson, MendePs Principles 

 of Heredity (Camb. Univ. Press. 1909), chap. x. 



2 Bestimmung und Vererbung des Geschlechtes (Borntraeger), 1907. 



3 G. Smith, Naples Monograph, Rhizocephala, 1906. 



