RECENT WORK ON THE DETERMINATION OF SEX. 1 



By Leonard Doncastee, M. A., 

 Fellow of King's College, Cambridge. 



[Note. — This paper was written in 1909. and much important work on the 

 subject has appeared since. It has only been possible to refer in footnotes to a 

 few of the more important of these papers. The additional notes and references 

 are inclosed in square brackets [ ]. It will be seen that some of the opinions 

 expressed may require modification in the light of our fuller knowledge. — 

 L. D. April, 1911.] 



At the Dublin meeting of the British Association the sections of 

 zoology and botany devoted a morning to a joint discussion on the 

 determination of sex. Some account of the opinions expressed has 

 appeared in reports of that meeting. 2 As in all discussions on this 

 subject, the speakers were divided into two groups, holding opinions 

 which at first sight appear irreconcilable. On the one hand there 

 was the school which maintains that sex is a property of the germ 

 cells and that after fertilization, if not before, the egg is irrevocably 

 committed to one or the other sex ; on the other there were representa- 

 tives of the influential body of biologists who prefer (he view that 

 sex can be influenced by external conditions and that the sex of any 

 individual is the result of a combination of forces, some tending in 

 one direction, some in another. Not many years ago the latter was 

 the prevalent opinion ; it was supposed that the fertilized ovum was 

 potentially bisexual, maleness being introduced by the spermatozoon 

 and femaleness by the egg, and that the sex of the developing 

 organism was determined by a variety of factors, the resultant of 

 which decided to which side the balance should incline. This idea 

 was supported by experiments on feeding the larvae of insects, frogs, 

 etc., in which it appeared that insufficient diet led to a higher pro- 

 portion of males than when the creatures were abundantly fed. But 

 critics have always pointed to the fact that these results might be 

 explained by differential mortality or other circumstances not allowed 



1 Reprinted by permission, with author's additions and corrections, from Science Prog- 

 ress, London, No. 13. July, 1909, pp. 90-104. 

 s Nature, Oct. 22, 1908, vol. 78, p. 647. 



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