THE DETERMINATION OF SEX. 41 



(/) Crustaceans. — In support of the same contention, Rolph has 

 drawn attention to the following among other facts. One of the brine- 

 shrimps {Artemia salina) resembles not a few crustaceans in the local 

 and periodic scarcity or absence of males, associated of course with 

 parthenogenesis. At Marseilles, Rolph says, this artemia lives in 

 especially favorable conditions, as its large size plainly indicates; there 

 it produces only females. Where the conditions of existence are less 

 prosperous, it produces males as well. "A certain maximum of 

 abundance and optimum of vital conditions in parthenogenetic ani- 

 mals — daphnids and aphides, Apus, Branchipus, Artemia, and 

 numerous other crustaceans — produce females; while less favorable 

 conditions are associated with the production of males." In regard, 

 however, to water- fleas (daphnids), it is fair to notice that Rolph' s 

 conclusions do not quite consist with Weismann's, who, with unique 

 experience in regard to these curious little animals, is disinclined to 

 allow the direct influence of temperature and nutrition in the matter. 



(g) Mammals. — When we pass to higher animals, the difficulties 

 of proving the influence of nutrition upon sex are much 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 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 proportion 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 favor of the same conclusion, — noting, for 

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

 lambs. He emphasizes 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. 



(Ji) 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 emphasized 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 



