The external genitalia of the female mole follow from the first a male type of development, the clitoris being long and peniform, and the uterovaginal canal having no outlet to the exterior. At each breeding season there is formed spontaneously a vaginal orifice which disappears soon after parturition.

The uterovaginal canal and uterine cornua increase enormously in length and breadth during the short intense breeding season, and rapidly atrophy to the normal size afterwards. When measurements of these organs are plotted, curves are produced which show graphically these changes.

The corresponding graph of ovarian weights docs not produce a similar curve, the maximum weights occurring during anœstrum, in whiter. The ovary in the mole consists of two parts, an ovarian part and a separate mass of interstitial tissue known as the “interstitial gland.” The maximum ovarian weights occurring in winter are due to hypertrophy of the interstitial gland and atrophy of the ovarian part of the ovary. In the breeding season the ovarian part increases in bulk and the interstitial gland atrophies, but the total weight of the ovary is diminished owing to the interstitial atrophy outweighing the ovarian activity. The two parts of the ovary thus undergo alternate rhythmic activity.

Previous workers have demonstrated the homology of the interstitial gland of the ovary with the testis of the male. The activity of the ovarian part of the ovary is now shown to correspond with the assumption of female function, and the activity of the interstitial gland to correspond with the cessation of female function and the assumption of male facies.

It is suggested that the female mole presents as a normal condition the phenomena of a type of intersexuality found only as an abnormality in most mammals, and the probable process of differentiation producing this state is discussed.