These experiments, of course, have been chiefly performed upon the lower animals. The frog has been a favorite subject of such experiments--the tadpole stage being the one selected, because in that stage there exists a lack of sex, the stage being one of sex neutrality. Professor Yung's celebrated experiments will illustrate this class of experiments. Here were chosen 300 tadpoles, which when left to themselves manifested a ratio of 57 prospective females to 43 prospective males. These were divided into three classes of 100 tadpoles each. Each class was then fed upon one of several kinds of nutritious diet in order to ascertain the change in sex-tendency due to such food. The first set, with an original ratio of femaleness of 54 to 46, were fed abundantly on beef, and the ratio of femaleness was changed to 78 to 22. The second class, with a ratio of femaleness of 61 to 39, were fed on fish (specially nourishing to frogs), and the ratio changed to 81 to 19. The third class, with a ratio of 56 to 44, were fed upon a still more nutritious diet (i. e., that of frogs' flesh), and the ratio was raised to 92 to 8. In short, the experiments showed that the increase of nourishment in diet changed every two out of three male-tendency tadpoles into females. The experiment was held to prove that a rich diet, affording nourishment, during the period of sexual neutrality in the embryo, tended to develop femaleness. The advocates of this theory also point to the instance of the bees. With the bees, the larva of ordinary worker-bees are fed ordinary food, and do not develop sex; while the larva which is intended to produce the queen-bee is fed specially nutritious "royal food," and consequently develops larger size and full female sex powers. If the queen is killed, or dies, the hive of bees proceeds to produce a new queen by means of feeding a selected larva with the "royal food" and thus developing full femaleness in it. It is said by some authorities that in cases in which some other of the larva accidently receive, through mistake, crumbs of the "royal food," they, too, grow to an extraordinary size, and develop fertility. This fact is held by the advocates of the nutrition theory to go toward establishing the fact that abundant nourishment of the embryo, during the neutral stage, tends to produce femaleness in it. They also claim that caterpillars which are very poorly nourished before entering into the chrysalis stage usually develop into male butterflies, while those highly nourished in the said stage tend to become females. Experiments on sheep have shown that when the ewes are particularly well nourished the offspring will show a large proportion of females.