It will be seen that not only do different cells for the different sexes develop themselves out of an ovum, but that also, at the same time with these, a peculiarity reveals itself in the other cells, in accordance with which the sexually different organisms exhibit a difference in their vital capacities, and take also different forms. The distinction between male and female characteristics appears to be determined before the fecundation of the ovum. The formation of the ova in the ovary, and their further development, seem, however, not to be independent of external influences. It is possible that upon these circumstances depend the number of ova contained in the ovary. But, apart from the question of quantity, it is possible that many characteristics might so affect the quality of the ovum, as to exercise an influence over its capacity for fecundation. We may here mention an experiment which was made with the ova of a rabbit, from which it was quite clear that the capacity of an ovum for fecundation was immediately diminished when the surrounding elements attached to the ovule, in consequence of the density of their investing substance, offered a resistance to penetration by the spermatozoa. (Schenk.) The penetration of a spermatozoon into the protoplasm of the ovum becomes possible only when, in consequence of the movements of the spermatozoon, the cells of the surface of the ovum can be thrust aside. This is facilitated when the investing substance is considerably relaxed, as is the case when the ovum is ripe. Other circumstances, also, which can in some cases be easily detected, may prove detrimental to fecundation and development. Indeed, they can even exercise an influence over the sex which is to be developed out of the ovum. Bee-masters (F. Gerstung) have frequently shown that the food exercises a striking influence upon the formation of sex in the ova. (v. Berlepsch.) All evidence goes to support the view that such external influences as would favorably affect the separate sexual individual might also promote the production of one sex or the other. In Hensen’s valuable work on generation, a number of instances are adduced, gathered from various authors, which make it clear that the nutrition of the parents, apart from any question of race, is capable of exercising an influence upon the sex of the children. (Ploss.) In plants which produce separate male and female blossoms (Lenkhart), the male blossoms are more numerous when the temperature is relatively high, whilst in shaded places and damp soils a greater number of female individuals will be observed. * * * * *