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. * * * * * These processes which take place at rutting time are attended with sexual excitement and congestion of the external genitals. It is not, however, necessary that these processes should in the case of all animals occur at the same time as ovulation. If rutting animals are restrained from sexual intercourse, the sexual excitement of the female passes off; but the symptoms of rutting again make their appearance after a time. These are the phenomena of the so-called rutting season. This rutting season lasts with sheep fourteen days, with swine fifteen to eighteen days; with cows, horses, and apes four weeks. It corresponds to the menstruation of the human female (Hensen). Many bitches admit the dog only when six or seven days have elapsed since the issue of blood. In the case of many animals rutting is marked by a flow of blood from the genitals. This is the case with apes, bitches, swine, and many other mammalia. * * * * *