648 THE PHYSIOLOGY OF REPRODUCTION 



by them in support of this hypothesis. The normal female 

 metabohsm is said to be relatively anabohc, while the greater 

 activity of the male is held to indicate a preponderance of kata- 

 bohc conditions. Consequently the generahsation is reached 

 that abundant or rich nutrition (or any other favourable circum- 

 stance) tends to induce an anabohc habit, and so favours the 

 development of females ; and conversely, that deficiency of the 

 necessary food supply (or any adverse circumstance) leads to a 

 katabohc condition of Ufe, and so causes the production of males. 

 According to this idea, the organism is at first " sexually in- 

 different," the sex becoming established at varying periods of 

 development in different animals according to the circumstances. 

 Thomson has recently admitted that some of the evidence 

 which was formerly adduced in support of this view has since 

 been invahdated, and that it seems being proved more and 

 more that sex is fixed in the fertihsed ovum or earlier, and 

 consequently that subsequent conditions of nutrition can play 

 no part in determining the relative proportion of males and 

 females. But Thomson is still disposed to lay stress on the 

 connection between sex and metabohsm, beheving that the 

 determinants for each of the sexual characteristics (both male 

 and female) are present in all ova and in all sperms, and that 

 their hberation or latency depends on a bias towards egg- 

 production or sperm - production. The so-caUed contrasted 

 pecuharities of the two sexes are due in certain cases " to in- 

 ternal physiological conditions which give the same primordium 

 two different expressions, much less different than they seem." ^ 

 Statistics of human births have been brought forward in 

 support of the view that the proportion of the sexes varies with 

 the conditions of nutrition. It has been pointed out that in 

 France the proportion of births of boys and girls is 104-5 to 100 

 for the upper classes (which are presumably best nourished) 

 and 115 to 100 for the lower classes (who are more poorly fed). 

 In the Almanack of Gotha the proportion recorded is 105 boys 

 to 100 girls, while for Russian peasants this proportion is 114 to 

 100. Among the nobihty of Sweden statistics show a proportion 

 of 98 male to 100 female births, but that given for the Swedish 

 clergy is 108'6 boys to 100 girls.^ There is therefore some 

 ' Thomson, Heredity, London, 1908. " See Morgan, toe. cit. 



