104 SCIENCE PROGRESS 



sex may be, it is conceivable that the proportion of germ-cells 

 bearing one or the other sex which come to maturity may 

 possibly be influenced by external conditions. To do justice 

 to what has been written on such subjects would require a book 

 of considerable size, and in the present paper is impossible. 

 The object of this account will have been fulfilled if it indicates 

 the direction in which recent work is leading and if it makes 

 it clear that the probabilities are overwhelmingly in favour 

 of the idea that the determination of sex is not consequent on 

 the accidental preponderance of one or other of two nicely 

 balanced tendencies but is due to fixed and unalterable characters 

 inherent in the germ-cells. 



