On various occasions, whilst taking into consideration the possibility of an influence on the part of the parents over the sex of the child (in such respects as have been placed before us in the literature dealing with this subject), we often had occasion to direct attention to the food of the parents. And especially the food of the mother seemed to us to be of the highest importance. Now, it is universally known that metabolism is increased during pregnancy. The products of excretion in the case of pregnant women are much smaller than the quantity of matter taken in, in the shape of food. The difference, to a great extent, represents the matter taken to form the bodily substance of the embryo, in accordance with the anterior laws which have been fixed by the doctrines of the physiology of metabolism. It will, then, be necessary to pay particular attention to the investigation of metabolism. Suggestions are not wanting. They will be found amongst the observations of leading specialists. For example, Winckel observed that during pregnancy the temperature was slightly raised. This increase of temperature must practically be explained as due to the higher and more productive process of oxidization, which has to be accomplished by the human female for the sake of nourishing the fœtus. During pregnancy the number of blood corpuscles suffers an observable diminution. Still plainer is the reduction of the quantity of hæmoglobin, when measured with Fleischl’s hæmatometer. This last phenomenon is very likely connected with a greater consumption of hæmoglobin, the substance being used up by oxidization. Observations of setting hens are not without interest. In their case, also, a diminution of hæmoglobin is observable during the period of incubation. The hæmoglobin can sink to nearly 50 per cent. of the normal amount. With the increase of hæmoglobin in the embryo and its simultaneous diminution in the mother during incubation, it happens, at a certain period in the process of development, that the embryo in the egg and the setting hen possess a nearly equal measure of hæmoglobin with a nearly equal number of blood corpuscles. An increase of the quantity of hæmoglobin until the normal amount is reached may be observed in both towards the end of incubation. The Rhine salmon each year go up in a well-nourished condition from the sea into the fresh-water streams to spawn. There they remain several months. They lose much of their muscular substance. (Miescher.) On the other hand, a great development of the sexual organs and of sexual secretions takes place, produced, probably, at the expense of the used-up muscular substance. Many have paid particular attention to the nourishment of the maternal organism. Investigations have also been published dealing with the nutrition of the parent animals in cases when it was desired to exercise an influence over the sex.