REPRODUCTION AND SEX 533 



Of great interest and importance are Russo's experiments in 

 treating rabbits with lecithin. They support the view that the 

 germ-cells may be predisposed to one sex or the other by the 

 nutritive condition of the parent, and the view that the difference 

 between the sexes is primarily a question of the rhythm of meta- 

 bolism. 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 believes that the sex of the offspring 

 depends on the special metaboHsm of the germ-cells; and he thinks 

 he has succeeded in artificially altering the metabolism of the 

 ovarian ova, and thus altering the normal proportions 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 Mercks' lecithin developed 

 large ovaries, large Graafian follicles, ova rich in nutritive material, 

 and eventually an unusual number of female offspring. The sperm 

 may, as it were, corroborate the bias of the ovum, for the percentage 

 of female offspring is higher when both parents are fed with lecithin. 

 It is not possible to follow the ova and prove that a relatively 

 anabolic ovum always becomes a female, and never a male, but 

 the argument from altered proportions seems sound. While the 

 lecithin treatment is followed by an increase in the number of ova 

 of "an anabolic type, rich in lecithin globules", it may happen that 

 the first litter after the beginning of the treatment shows a marked 

 preponderance of males. This Russo regards as due to the fact that 

 the injections stimulate the general metabolism and inhibit the 

 degeneration of the ova of the katabolic type, capable of producing 

 males. The increase in the number of females occurs subsequently. 



Several investigations support the view that changes in nutrition 

 and other environmental conditions may affect the mother so as to 

 alter the ordinary proportions of the sexes. Thus Issakowitsch, 

 working with the parthenogenetic females of the Daphnid Simo- 

 cephalus, and von Malsen, working with Dinophilus apatris, in 

 which the ova are fertilised, found that differences of temperature 

 affected the proportion of the sexes, apparently by affecting the 

 nutrition of the mothers. Both sets of experiments are the more 

 satisfactory that they seem to be free from any fallacy due to 

 differential death-rate in the young of the two sexes. 



Against the theory of environmental influence are Strasburger's 

 numerous experiments on dioecious Phanerogams, such as Mercu- 

 rialis perennis, spinach and hemp. He found that changes in illu- 

 mination, soil, crowding, and so on, had no effect in altering the 

 proportions of male and female offspring. 



As regards the fifth theory, then, we find: (i) that in certain cases 

 there is some evidence that the nurture of the parents may influence 



