THE DETERMINATION OF SEX. 47 



greater. Yet there are decisive observations which go to increase 

 the cumulative evidence. Thus an important experiment was 

 long ago made by Girou, who divided a flock of three hundred 

 ewes into equal parts, of which the one-half were extremely 

 well fed and served by two young rams, while the others were 

 served by two mature rams and kept poorly fed. The propor- 

 tion of ewe lambs in the two cases was respectively sixty and 

 forty per cent. In spite of the combination of two factors, the 

 experiment is certainly a cogent one. Diising brings forward 

 further evidence in favour of the same conclusion, noting, for 

 instance, that it is usually the heavier ewes which bring forth 

 ewe lambs. He emphasises the fact, that the females having 

 a more serious reproductive sacrifice, are more dependent on 

 variations of nutrition than males. Even in birds, as Stolzmann 

 points out, there is a much greater flow of blood to the ovaries 

 than to testes, — the demands are greater, and the consequences 

 therefore more serious if these are not fulfilled. 



{h) In the human species, lastly, the influence of nutrition, 

 though hard to estimate, is more than hinted at. Ploss may 

 be mentioned as an authority who has emphasised this factor 

 in homo. Statistics seem to show, that after an epidemic or a 

 war the male births are in a greater majority than is usually 

 the case. Diising also points out that females with small 

 placenta and little menstruation bear more boys, and contends 

 that the number of males varies with the harvests and prices. 

 In towns, and in prosperous families, there seem to be more 

 females, while males are more numerous in the country and 

 among the poor. 



(/) Deteri?imation of Sex in Plants. — It is at present ex- 

 tremely difiicult to come to any very satisfactory conclusion in 

 regard to the influence of nutrition upon the sex of plants. 

 The whole subject, as far as its literature is concerned, has 

 been recently discussed by Heyer, but his survey is by no 

 means a sanguine one. His conclusions, in fact, seem to land 

 him in a scepticism as to all modification of the organism by 

 environmental influences, which we should of course be far 

 from sharing. It must be admitted that the experiments of 

 Girou (1823), Haberlandt (1869), and others, yielded no cer- 

 tain result; while the conclusions of some others, are conflicting 

 enough to justify not indeed Heyer's despair, but his present 

 caution. Still a few investigations, especially those of Meehan 

 (1878), which are essentially corroborated by Diising (1883), 



