It is not, however, shown what the systems are by which such an ovum can be correctly judged, so as to determine the different degrees of ripeness. We now know very well certain signs which appear upon the maturation of the ovum, of which we shall not say more here. Of these Thury could know nothing in 1863, because at that time they had not been discovered.
Thus the sex depends upon the ripeness of the female’s ovum at the time of its fecundation. In the case of its having reached the highest degree of ripeness, a male is the result. It is impossible for the ovum to attain a higher degree of ripeness. If the ovum of a human female has arrived at this supreme degree of ripeness, it has reached that stage in which it is capable of becoming the basis of the most perfect living creature which exists upon our globe.
Rutting is an external sign of the maturity of the ovum amongst the lower animals. When, during the rutting period, an ovum is detached from the ovary, and passes through the Fallopian tubes to the cavity of the uterus, the fructification can take place at the beginning of the rutting period. At this period its ripeness is not so far advanced. The result of the development of such an ovum is a female. But when the fecundation has taken place at the end of the rutting period, the ovum has reached its highest degree of development, and, if effectively fecundated, it will become a male. It follows that the signs of rutting should be carefully studied, as in fact is habitually done by practical farmers. The duration of the rutting period and the influences which affect fertilization should be accurately known in order to lead to any practical result.
Females at their first conception would usually produce, or would be particularly disposed to produce, female individuals. Experiments succeed better with such as have often produced young. In their case the symptoms which indicate the commencement or the conclusion of the rutting are much more easily determined, so that they are better adapted for these experiments.
We know well that in the case of the lower animals when rutting, as in the case of the human female during menstruation, an ovum is liberated from the follicle in the ovary, and ordinarily passes away in the menstrual discharge. In fact, a follicle of the ovary bursts, and, to be precise, that one which protrudes most beyond the surface of the ovary. This bursting of the follicle has not actually been observed. But that this event takes place there can be no doubt, for the locality of the fissure is perceptible, and the ovum is found either at hand on the ovary, or else on the fimbria. The increase of fluid in the follicle of the ovary, and the excessive charge of blood in the vessels on the walls of the follicle, seem to be, without any actual contraction taking place, the physiological causes of the freeing of the ovum from the follicle, so that it may come in contact with the semen. Ovulation can take place without intercourse. But sexual intercourse can also favor ovulation; at least, it appears to facilitate the separation of the ovum from the ovary.
Bischoff made known the fact of the separation of the ovum from the follicle. He showed that the presence of sperm in the feminine organs of generation of the animals was indifferent, that the rutting of the animal was the index of the ripeness of the ovum. Eimer, Beneke, Van Bamecke, and Hensen, call attention to the phenomenon which is observed in the case of bats, who for a whole month before the detachment of the ovum from the follicle have their uteri full of semen.