The President's Address. By J. Arthur Thomson. 159 



determines sex is a metabolism-rhythm, or a relation of nucleo- 

 plasm and cytoplasm, or a relation between Anabolism and 

 Katabolism. 



Many sets of facts lead one to suppose that each sex-cell has a 

 complete equipment of masculine and feminine characters, and it 

 may be that the liberating stimulus which calls the one set or the 

 other into expression or development, is afforded by the metabolism 

 conditions that have been set up in the field of operations, which 

 lead also to the establishment of ovary or spermary, as the case 

 may be.* 



That the fundamental thing is a physiological alternative is 

 suggested in various ways. For instance, there is the sometimes 

 striking evidence that sex is " a quality that pervades all the cells 

 of the organism." Professor Wilson notes that, " In the Mosses the 

 Marchals demonstrate that all the products of a single spore are 

 likewise immutably determined, since new plants formed by regene- 

 ration from fragments of the protonema, or from any part of the 

 gametophyte, are always of the same sex." 



It must be remembered that many at least of those who are 

 keenest on the scent of morphological criteria are also alive to the 

 importance of trying to get at the physiological realities behind 

 these. Thus we find Professor Wilson saying, " Since the two 

 classes of spermatozoa differ in nuclear constitution it is highly 

 probable that they differ in respect to their metabolic processes." 

 Or, again, " Upon what conditions within the fertilized egg does the 

 sexual differentiation depend ? In some way, we may now be 

 reasonably sure, upon the physiological reactions of nucleus and 

 protoplasm." 



And I may be pardoned, perhaps, for quoting from a recent able 

 article by Professor H. E. Jordan, the last paragraph : " The results 

 of the newer investigations on sex -determination seem, at least tem- 

 porarily, to have brought us back to the position of Geddes and 

 Thomson, namely, that femaleness is causally related to a dominat- 

 ing cell-anabolism, and maleness to a relatively preponderant cell- 

 katabolism. This conclusion would seem to be the base from which 

 future investigations will start in the attempt to further elucidate 

 the fundamental mechanism of sex-differentiation." 



* When this was written I had not enjoyed the pleasure of reading Dr. C. E. 

 Walker's Hereditary Characters (1910). In the chapter on " Sex and Natural Selec- 

 tion " he says (p. 207), "The evidence then seems to suggest that the secondary 

 sexual characters are dependent for their development upon the presence of the 

 sexual glands in the individual, and that the potentiality of producing them is 

 present in all individuals of both sexes." 



M 2 



