Pagenstecher remarks that the relations which have existed anterior to the fertilization of the ovum, as well as its age (with which its ripeness is connected), are from the outset without influence on sex. The embryonal germ, before its fertilization, is an embryo whose sexual development is undetermined. In this case fertilization acts as an external factor in the direction of determining the sexual quality of this indeterminate embryo. The act of impregnation would be of influence upon the sex of the embryo in accordance with the character of the father. That follows from Pagenstecher’s explanations of Hofacker’s observations. According to Hofacker we get from men of twenty-four years of age and upwards, as also from sheep of a certain age, an average of a greater number of males. In the case of mothers, also, as we have already pointed out, the sexually-stronger age (Lenkart, Girou de Buzareingues, Hofacker, Morel de Vindé, Sadler) and the food have an influence upon the majority of births of female individuals. Here should be added the experience of Nasse and Van den Bosch. The observations of Dzierzon, von Siebold, Lenkart, and von Berlepsh, on the development of sex in bees, and, according to von Siebold, among the Psychids, should also be taken into consideration. When the females of certain Psychids are not impregnated they lay only female ova. If they are impregnated, male ova appear also. The tree-lice (Cestoni, Réaumur) give birth to living young without impregnation. These are at first only female, _afterwards males appear as well_. After this impregnation commences, and the females begin to lay ova. The experiments of Knight, who found that melons and cucumbers produce male blossoms under higher temperature and female under lower (which was verified by Mauz), demonstrate that, in this case, such external factors as warmth, light, dryness, have an influence upon sex. Pagenstecher, however, believes that the conditions of origin of sex are not the same in animals and plants. We must not, he says, from these observations draw conclusions off-hand respecting the sexual propagation of plants nor of animals in general. It must be further pointed out with regard to the thesis that ova which are emitted last have had more time to ripen, that we must reflect whether the process of ripening may not have also begun late. Thury’s observation that the last egg laid by a singing bird developed a male (communicated by O. Bourrit), and that in the case of hens the majority of the later eggs were males, seemed to Pagenstecher not quite certain. He mentions also a method by which, in poultry breeding, the breeding experiments can be conducted on a regular principle, which I shall quote word for word:--