320 riddle: control of sex ratio 



appearance just as well without it Sex, therefore, al- 

 though it is almost universally found, cannot be said with certaintj' 

 to be a necessary attribute of living things, and its real nature remains 

 an apparently impenetrable mystery. 



From the statements of this rather long quotation we shall 

 have occasion, during the present hour, to dissent only from the 

 impression that the problem of the nature of sex offers difficul- 

 ties of a magnitude comparable with those touching the origin 

 of life, and that its mysteries are apparently impenetrable. 



Studies on the heredity of sex have indeed made great prog- 

 ress during the last fifteen years. These studies have been con- 

 cerned with sex-linkage and with the so-called sex-chromosomes. 

 Since Doncaster, whom I have quoted, is one of the foremost 

 workers in both of these fields of study, it is particular^ signifi- 

 cant that, in his opinion, all of the results thus far obtained from 

 breeding and cytology have thrown so 'little light on the real 

 nature and meaning of sex, and that from further advances in 

 these fields he apparently hopes for so little. For this reason — 

 and another, namely that the relation of chromosomes to hered- 

 ity and sex, have probably been extensively treated in other 

 lectures of this series — you will, I trust, not now require a lengthy 

 survey of the relations which the chromosomes are known to bear 

 to sex, but will grant most of the present hour for an examina- 

 tion of the results obtained from studies of a quite different sort ; 

 namely, of experimental attempts to control the sex ratio, to 

 learn the nature of sex, and to control the development of sex. 



It is quite necessary, however, that all experimental studies 

 on the control of the sex ratio should be carried out with the 

 fullest recognition of the known normal association of the chro- 

 mosome numbers — particularly of the sex-chromosomes — with 

 sex, if the results of such studies are to be used toward a decision 

 of the question whether sex itself has been reversed or controlled. 

 The all-important question concerning abnormal or unusual sex 

 ratios is, of course, the question of their meaning — Has a par- 

 ticular germ cell which had initial tendencies to produce one sex 

 been experimentally forced to the production of the opposite 

 sex? Or — a quite different thing — have the conditions of the 



