With the views of Robin may be connected also other suggestions regarding the food of the parents. These have been tried both with men and animals. But we shall not here go further into them. Nor shall we mention the different kinds of food or drink which have been employed, whether by men or women, to produce a greater sexual activity. * * * * * The eminent naturalist Born, of Breslau, made a long series of experiments, which are of the highest interest in reference to the doctrine of the origin of sex. It is easy to fertilize frogs’ eggs artificially. The ripe eggs are taken directly from the female, and the testicles of the male rubbed with water. This fluid, which now contains spermatozoa, serves to fertilize the eggs. Spallenzani had already undertaken artificial fructification. Born observed, during his study of the course of development, that the effect of his breeding as regarded sex was to produce 95 per cent. of females. This number is evidently so remarkable that it ought to secure particular attention. No such extreme contrast between the numbers of males and females is to be found amongst the frogs that develop freely under natural circumstances. It seemed to Born that his result was to be referred to insufficient nourishment, and that the tadpoles, being somewhat unfavorably circumstanced, had not been able to attain the development of the stronger sex. In this experiment on the evolution of sex it appeared that not only was there an excessive production of females, but that the other organs of the embryo and its whole constitution could be modified by means of nutrition. It is also to be observed respecting this most interesting experiment that many of the tadpoles perished of hunger. Now, the number of still-born males of the human species very much exceeds the number of still-born girls. The mortality amongst males is so great that the average is from 136 to 140 still-born boys to 100 still-born girls. An attempt has been made (Pflüger) to explain this phenomenon in the human subject on the ground that the tenacity of life in the female sex in the period of embryonal existence exceeded that of the male. Consequently, boys would more easily perish during development than girls. If this observation made with respect to human beings were applied to the tadpoles, it might also explain the high percentage which the females showed among the frogs. Very likely the male tadpoles possessed less capacity of resistance; or, in other words, were less tenacious of life than the females. It will be understood that this view would apply only as a partial explanation of the facts set forth by Born. * * * * *