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.
Under these circumstances, the symptoms of rutting are sufficiently distinctly marked to make it possible, as Thury suggests, to determine the advanced state of ripeness or its commencement in the ova. But it is scarcely possible to say when the period of ripeness commenced in this ovum or that. An ovum which had begun to ripen early may, at the beginning of the rutting time, have attained to the condition of a male-producing ovum. At the same time, others which are fertilized at the conclusion of the rutting, but had begun to ripen comparatively late, may, at the end of the rutting time, not yet have advanced far enough to be able to develop male individuals.
Thury bases his doctrine on a number of phenomena of the vegetable and animal world, and upon various experiences in the case of man. He also adduces many statistical data in explanation and support of his theory.
The observations on plants make it indisputably clear that all the circumstances which favor growth and ripening are favorable conditions for the development of male organs. If all these circumstances are lacking, female organs are produced.
Dark and cold, for instance, cause the male organs to perish. In recent times a great number of extended studies of the phenomena of vegetable life in this direction have appeared. I may mention more particularly the following experiments made by M. von Treskow in Gorlitz with Arisæma (Verhandlungen des Botanischen Vereins der Provinz Brandenburg, 1895). This plant first produces male flowers. In the later year, when it has become larger, it produces female flowers. The transition from the male flowers of the early stage to the female flowers of the later stage can be hastened at pleasure by planting in rich garden mold and manuring with horn shavings. If, on the other hand, the plant be placed in poor, sandy soil, it reverts to the male flowers. The same author quotes in his essay a remark of Heyer’s (Halle, 1884), who declares that no sufficient observations exist respecting the influence which different situations exert over sex.