502 HEREDITY AND SEX 



in which all the eggs were hatched, the percentage of males 

 produced was more than three times that which was obtained 

 from the other aviary, in which the environmental conditions 

 were less favourable. The results obtained in each case could 

 not be ascribed to the particular strains of canaries, since an 

 interchange of birds between the aviaries was not followed by 

 any material alteration in the proportion of the sexes in the two 

 environments. It is concluded, therefore, that . the ova were 

 subject to a selective action on which depended the proportional 

 differences produced " (The Physiology of Reproduction, 1910, 



P- 645). 



As the facts stand at present, they point to the conclusion that 

 if nutritive and other environmental influences are operative, 

 it is, in the main, by affecting the production and the survival of 

 sexually-predestined germ-cells. 



Of great interest, and, as it seems to us, of importance are 

 Russo's experiments in treating rabbits with lecithin. They lend 

 support to the view that the germ-cells may be predisposed to 

 one sex or the other by the nutritive condition of the parent, 

 and to the view that the difference between the sexes is primarily 

 a question of the rhythm of metabolism. Russo attaches much 

 less importance to the chromosomes and much more importance 

 to the nature of the metabolism than do most biologists of to-day. 

 He says, in so many words, that he believes the sex of the off- 

 spring to depend on the specific metabolism of the germ-cells ; 

 .and he thinks he has succeeded in artificially altering the meta- 

 bolism of the ovarian ova, and thus altering the normal propor- 

 tions of the sexes. In the normal ovary there are well-nourished 

 and ill-nourished ova, and the proportion of the former can be 

 increased by lecithin treatment. 



Female rabbits treated by injections of Merks' lecithin 

 (solution of 15-20 per cent, in vaseline oil) developed large ovaries, 

 large Graainan follicles, ova rich in nutritive material, and eventu- 

 ally an unusual number of female offspring. The sperm may, as 



