254 GENETICS AND EUGENICS 



mete furnished by the father is therefore the smaller gamete, 

 the so-called micro-gamete. 



From the standpoint of metabolism, the female is the more 

 advanced condition: the female performs the larger function, 

 doing all that the male does in furnishing the material basis 

 of heredity (a gamete), and in addition supplying food for the 

 embryo. As regards the reproductive function, the female is 

 the equivalent of the male organism, plus an additional func- 

 tion, — that of supplying the embryo with food. When we 

 come to consider the structural basis of sex, we find, often in 

 differences in chromosome number, reasons for thinking that 

 here, too, the female individual is the equivalent of the male 

 plus an additional element.^ The conclusion has very natu- 

 rally been drawn that if a means could be devised for increas- 

 ing the nourishment of the egg or embryo, its development 

 into a female should be thereby insured, while the reverse 

 treatment should lead to the production of a male. 



In a few cases it has been found possible by indirect means 

 to control the state of nutrition of the eggs and so to control 

 the sex of the individual which develops from it. Thus in the 

 rotifer, Hydatina senta, parthenogenetic eggs of two sorts 

 are produced, which are either male-producing or female- 

 producing, the former being smaller. Whitney has shown 

 that when a colony of Hydatina is fed for a generation exclu- 

 sively on the green flagellate, Dunaliella, practically all the 

 mothers lay male-producing eggs, but a continuous diet of 

 the colorless flagellate, Polytoma, leads to the production of 

 female eggs. The effect in each case is seen not in the first 

 generation, but in the second generation of offspring. The 

 female fed on Dunaliella has grandsons; the female fed on 

 Polytoma has granddaughters. The diet of the mother is 

 immaterial. 



In pigeons, eggs are produced in clutches of two each, and 

 in wild species these commonly develop, one into a male, the 



^ But in the poultry type qf sex -linked inheritance it is evident that the male is 

 more liberally equipped with certain genes, in which he is duplex while the female 

 is simplex. 



