The absence of ovaries has been often noticed in twin heifers, and most commonly associated with deficiency or absence of the womb, and even of the anterior part of the vagina. The condition is especially common, though not constant as some have supposed, when the other twin was a male. Such females are known as _free martins_ and fail to breed. Even when the ovaries are present in such twins they remain undeveloped, and are no larger than a bean or hazel nut. These usually have a firm, fibrous structure, and though there may be interspaces filled with a transparent fluid, no true Graafian follicles are formed. In birds, the left ovary only is developed and physiologically active. The absence of ovary has been noted also in the ewe, and less frequently in the mare and other species, and appears to be more common in twins than in single pregnancy. In cattle only has the influence of the male on the female twin of the same pregnancy been specially noted. It has been noted that females with ovaries undeveloped, tend to show many male characters, in head, horns, and neck in cattle, in plumage in birds, and in voice in both. ATROPHY OF OVARIES. This is observed as a physiological result of having passed the breeding age, and may also take place from disease and degeneration of the organ. The fibrous stroma is usually increased and the cell elements reduced, yet in some cases, a cystic development occurs, giving the appearance of hypertrophy, while the ovarian parenchyma has actually been diminished. SUPERNUMERARY OVARIES. Extra ovaries have been found in different cases in the human female, the additional organ being furnished with a fallopian tube, and in some instances an extra uterine horn. No facts are at hand concerning the lower animals, but the occurrence of gestation and the birth of a single puppy a year after careful castration, would seem to suggest that the condition occurs in the bitch. There is no embryological reason why the lower animals should not at times show this deviation from the normal. IRRITABLE OVARY. NEURALGIA OF THE OVARY.