10 



THE SEX-COMPLEX 



Effect of en- 

 vironment 

 and nutrition, 



Sex-determ- 

 ination at 

 fertilization. 



Sex-determ- 

 ination sub- 

 sequently to 

 fertilization. 



and usually vigorous — sons are more numerous than 

 daughters ; on the other, it has been believed x that, 

 after the stress and indifferent nutrition which may 

 result from a long war, male infants have been born in 

 greater numbers than females. 



It is, however, almost impossible to obtain reliable 

 statistics regarding the influence of nutrition, environ- 

 ment and other indirect causes on the sex of the off- 

 spring, because the factors concerned are often mixed 

 or conflicting, and because infantile mortality plays 

 such a large part in the final or apparent result — that is 

 to say, in regard to the sex-ratio among adults. Be 

 this as it may, the general opinion is held that under 

 favourable conditions female births preponderate, and 

 in unfavourable circumstances male. 



(2) The view that sex is determined at fertilization is 

 also founded on biological evidence, for it is known that 

 male bees and the males of certain other insects are 

 developed parthenogenetically from unfertilized ova, 

 while the females are produced from those which have 

 been fertilized. 



Schenk 2 and others have asserted that sex-determina- 

 tion depends on the state of the nutrition of the ovum at 

 the time of fertilization. This view was elaborated by 

 Schenk, who claimed that by supplying the mother with 

 a nitrogenous diet before conception he could increase 

 the chance of the offspring being a male. Time, how- 

 ever, has shattered these pretensions concerning the 

 practical application of this theory, whether or not there 

 be any substratum of truth in it. 



(3) We now come to the last view ; namely, that 

 sex is determined subsequently to fertilization. 



It has been demonstrated by Yung 3 that in tad- 

 poles sex is not determined until late in that stage of 

 the development of the frog ; and evidence has been 

 obtained that nutrition affects the final outcome. 



1 Geddes, P., and J. A. Thomson, Sex, 1914. 



2 Schenk, L., The Determination of Sex, Eng. Trans., 1898. 



3 Yung, E., Compt. Rend, de VAcad. dea Sci., 1881, vol. xciii, p. 562. 



