228 BIOLOGY: GENERAL AND MEDICAL 



Sex Determination. A peculiarity of development to 

 which no reference has thus far been made is that of the 

 sex of the individual, and as it is of importance for the 

 safety of the species that the number of individuals of 

 each sex be properly proportioned, it becomes a matter 

 of considerable interest to discover, if possible, how the 

 sex of each individual is determined. 



The question has received attention from early times, 

 and the number of theoretical explanations that have been 

 suggested corresponds with the obscurity and difficulty 

 of the problem. "Blumenbach, in his fascinating brochure, 

 'Ueber den Bildungstrieb/ points out that Drelincourt 

 brought together two hundred and sixty-two groundless 

 hypotheses of sex, that had been proposed, and Blumen- 

 bach remarks, quaintly, that nothing is more certain than 

 that Drelincourt's own theory made the two hundred 

 and sixty-third." 



At the present time, through cytological studies, we are 

 no doubt much nearer to the truth than at any time in 

 the past, though we are still unable to formulate a theory 

 of sex determination that is generally applicable. 



An analysis of the writings upon the subject may be 

 briefly synoptized as follows: 



I. Theories diminishing in validity with increasing 



knowledge of cytological science. 

 1. That sex determination depends upon conditions 



entirely apart from the germinal cells. 

 A. That the sex of the offspring is determined by 



the condition of the parents: 

 (a) By the age of the parents. Sadler taught 

 that the sex of the offspring was in large meas- 

 ure determined by the age of the father. He 

 collected statistics that seemed to show that 

 the older the male parent was the greater the 

 number of male offspring he produced. 

 (6) By the vigor of the parents. Popular belief, 

 said to be based upon results obtained in breed- 

 ing domestic animals, has led to the opinion 



