riddle: control of sex ratio 355 



sexes is of equall}' wide distribution in that sexual differentiation 

 results from metabolic differentiation, through the establish- 

 ment of two relatively distinct and relatively stable levels of 

 metabolism. In the same way is accounted for the hitherto 

 puzzling fact that the two sexes must have originated many 

 times, scores, hundreds, or thousands of times, within species 

 previously unisexual, during the long period involved in the 

 evolutional history of organisms. 



Most important of all, perhaps, is the demonstration that one 

 hereditary character is modifiable, is of a fluid, quantitative, re- 

 versible nature. Seemingly this can only mean that other heredi- 

 tary characters are also modifiable. The methods and results of 

 most studies in modern genetics have asked us to accept a quite 

 different view, namely that no such thing as control of heredity 

 may be hoped for, but that we can only look to a sorting and 

 elimination of germs, or of so-called hereditary factors — and to 

 fortuitous origins or recombinations of the latter — to give us 

 better or more desirable organisms. Surely there is a lot of 

 fatalistic philosophy in that conception. All other aspects of 

 function in biology recognize — and some have already attained 

 —the control of life-processes as their aim and goal. Only in 

 this field of heredity — involving the overwhelmingly important 

 processes of continuance and of becoming — has this aim been 

 accepted by a great and growing body of workers as impossible. 

 If sex has been in fact controlled, if it has a modifiable metabolic 

 basis — as now seems assured — then the life processes involved in 

 heredity like other life-processes, invite the investigator to his 

 full and complete task; territory hitherto labelled '"impossible" 

 is open to investigation. 



BIBLIOGRAPHY 



Baltzer, F. Arch. f. Zellforsch., vol. 2, 1909. 



Baltzer, F. Mitteil. Zool. Stat. Neapel., vol. 22, 1914. 



Baxta, A. M. Year Book, Carnegie Inst. Wash., 1915. (Also Proc. Nat. Acad. 



Sci., vol. 2, 1916.) 

 Bell, A. G. Quoted from Popenoe. Jour. Hered., vol. 5, p. 47, 191 t. 

 Benedict, F. G., and Emmes, L. E. Jour. Biol. Chem., vol. 20, 1915. These 



authors give full references to the earlier literature. 



