544 GENETICS IN RELATION TO AGRICULTURE 



difference between the sex-ratio late in heat and early in heat can we 

 place any confidence in the significance of the observed differences. In 

 this case the odds are practically 19 to 1 against the chance occur- 

 rence of the deviation : the question thus presents itself for consideration, 

 shall we regard this difference merely as a chance occurrence or as 

 possessing real significance? We are informed that more recent data 

 (unpublished) according to Pearl make the relation of time of service 

 to sex extremely doubtful. Moreover, Pearl and Salaman have shown 

 that this relation does not hold for man. 



Metabolic Theories of Sex-determination. Among other theories 

 of sex-determination which have been advanced that of Geddes and Thom- 

 son still provokes a considerable amount of speculation and discussion. 

 According to this theory there is no sex-determinant or factor at all, in 

 the strictly Mendelian sense of the word, but rather differences in meta- 

 bolic relations lead to the production of different sexes. The theory is 

 based on the conception that deep constitutional differences in metabol- 

 ism- rythms exist between the two sexes; the male being characterized by a 

 preponderance of katabolic or disruptive processes, whereas the female is 

 distinguished by the emphasis placed upon constructive or anabolic 

 processes. 



It should be pointed out, and indeed Geddes and Thomson fully ap- 

 preciate this fact, that this theory is a physiological theory of sex-deter- 

 mination, whereas the Mendelian theory is essentially morphological. 

 The two are not necessarily in conflict with each other, so that an 

 acceptance of the conclusion that differences in metabolic balance exist 

 in the two sexes, does not necessarily imply rejection of the Mendelian 

 theory of sex. It is only when supporters of this physiological doctrine 

 argue for the possibility of sex-determination occurring after fertilization, 

 or in other words, for reversal of sex as fixed at fertilization by the in- 

 fluence of external factors operating subsequently to fertilization that 

 difficulties between the two views arise. Thus to take a particular case, 

 Pearl and Parshley on the basis of their statistical study of sex-deter- 

 mination mention the possibility of changes occurring in the metabolic 

 conditions in ova corresponding roughly to different periods in the time 

 of heat, and that by virtue of these changes alterations of the sex-ratio 

 might occur. But this suggestion carries with it reversal of potential sex 

 as determined by chromosome relations at the time of fertilization. We 

 may ask, therefore, with justice what sort of males are these which arise 

 from such alteration of metabolic balance? Presumably staleness 

 should not lead to extrusion from the egg of an entire chromosome, or 

 should not in the light of present day conceptions of factor stability lead 

 to changes in the factors of the sex determining chromosome. If, there- 

 fore, staleness leads to a change in the relations between nucleoplasm and 



