RECENT WORK ON THE DETERMINATION 



OF SEX 



By LEONARD DONCASTER, M.A. 

 Lecturer on Zoology in the University of Birmingham 



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. 1 As in all 

 discussions on this subject, the speakers were divided into two 

 groups holding opinions which at first sight appear irrecon- 

 cilable. On the one hand there was the school which maintains 

 that sex is a property of the germ-cells and that after fertilisa- 

 tion, if not before, the egg is irrevocably committed to one or 

 the other sex; on the other there were' representatives of the 

 influential body of biologists who prefer the 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 fertilised 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 proportion 

 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 for by the experimenters ; as we shall see, there 

 is such a mass of evidence accumulated on the other side that 

 this idea is now largely abandoned by biologists. 



But although the doctrine that sex may be influenced by 



1 Nature, October 22, 1908, vol. Ixxviii. p. 647. 



90 



