348 B. F. KINGSBURY 



The assumption — to speak in Mendelian terms — that the female 

 is homozygous (homogametic, Wilson; 9 9) as to sex, the male 

 being heterozygous (digametic, Wilson cf), which appears to be 

 the more generally accepted view, does not seem to afford a satis- 

 factory hypothetical basis for the explanation of the double 

 development of the reproductive duct system of higher verte- 

 brates, the prostate and rete ovarii in the female, the mammary 

 gland in the male. Nor does the converse furnish an interpreta- 

 tion much more satisfactory — that the male is homozygous as to 

 sex ( cf cf ), the female being heterozygous { 9 d"). If it is believed 

 to be of advantage to express sex in these terms, in so far as the 

 explanation of the development of the primary sexual characters 

 of vertebrates is concerned, it would seem necessary to consider 

 both male and female heterozygous as to sex, the male characters 

 being or becoming dominant in the male, the female characters 

 recessive, and vice versa, in accordance with the early sugges- 

 tion of Castle. 



The only generalization that can be safely 'drawn, however, 

 from the cytological conditions that have been described would 

 appear to be that in the development of the female sex a greater 

 amount of 'formative material' is required. This is in general 

 accordance with the suggestions of Boveri, Goldschmidt and 

 Wilson, and is supported by the experimental work of R. Hertwig 

 and Kuschakewitsch, Miss King, and Riddle, indicating what has 

 been termed a 'quantitative' rather than a qualitative factor in 

 the determination of sex. It would seem as though on the cyto- 

 logical side little assistance were to be gained from the work upon 

 the 'sex' chromosomes as carriers or determiners of sexual char- 

 acters. In most of the work upon the 'x, ' 'sex' or heterochro- 

 mosomes, the point of departure has been the correlation of 

 chromosomes or parts of chromosomes with the appearance in 

 development of definite morphological characters. The problem 

 of the early development in vertebrates of the reproductive organs 

 appears to be closely linked with hermaphroditism in the pattern, 

 which I believe — admittedly by Wilson — presents difficulties from 

 the standpoint of chromosomal sex determination. The problem 

 is, I believe, broader and there is involved the choice between what 



