JOUKNAL 



OF THE 



ROYAL MICROSCOPICAL SOCIETY. 



APRIL, 1911. 



TRANSACTIONS OF THE SOCIETY. 



VI. — The President's Address : The Determination of Sex. 

 By J. Arthur Thomson, M.A. 



(Delivered January 18, 1911.) 



I have taken as the subject of my Address, not without much 

 hesitation, one of the great unsolved problems of Biology — The 

 Determination of Sex. Though the subject cannot be discussed 

 with thoroughness within the compass of an Address, I hope to be 

 able to make clear what the general trend of investigation has been, 

 and what the present position of the question is. The particular 

 appropriateness of the subject on this occasion is to be found in 

 the fact that several of the most marked steps of progress in the 

 investigation have been due to microscopic work of the finest kind. 

 There is also a personal appropriateness, for I have taken a great 

 interest in the subject since I shared in the responsibility of 

 writing " The Evolution of Sex " more than twenty years ago. It 

 seemed to me natural and useful that I should state something of 

 what I know of the crop of investigations in regard to this 

 extremely important problem, and indicate what, in my opinion, 

 are the most promising recent developments. 



The Determination of Sex. 



1. From ancient times a keen interest has been taken in the 

 question of the determination of sex — the settling of the sex of 

 the offspring ; and the numerous suggestions offered in answer 

 might almost serve as an index of the progress of natural know- 

 ledge. For there were theological and metaphysical answers to 

 the question, before it began to be approached scientifically ; and 

 even after the problem was recognized as one that must be tackled 



April 19th, 1911 l 



