Formerly there was ascribed to the ovaries, in a lump and without qualification, an absolute despotism over the specifically feminine functions of menstruation, gestation, parturition, and lactation. Nowadays, we see its domain as a limited monarchy, if not indeed as one sovereign state of a republic, a member equal but not superior to the others of a board of directors. Its true business comes down to two particular rôles: first, the production of ova, and, second, the secretion of a hormone or hormones. Over the other functions once supposed its monopoly, all the ductless glands rule. What concerns us now is its internal secretion or secretions. One of them is known as lutein and it has never been chemically isolated in its pure form. The existence of lutein, like the existence of electricity, is an inference, something we are sure is there because of its effects. It originates in a remarkable part of the ovary, the corpus luteum. Besides, there are the products of the interstitial cells, the creations of a special layer of cells around the ovum, the membrana granulosa. They produce a substance tonic to the uterus. When the ovaries are removed, there occurs an atrophy of the womb muscle, due to loss of this tonic substance. This atrophy, accompanied by an abolition of the normal periodic uterine contraction, makes conditions unfavorable to pregnancy. It has been claimed that the secretion of the corpus luteum is necessary for the complete progress of a pregnancy. Cases are on record, however, of ovaries taken out soon after the onset of pregnancy, without interference with the gestation. Castration is comparable in every way with the menopause or the time of cessation of sexual life, a process that might be called self-castration. It produces certain general constitutional effects. Adiposity often develops, undoubtedly associated with underfunction of the thyroid and pituitary glands. The woman breathes less oxygen per minute and burns up less food and tissue. There is some disturbance of the lime balance with an increased excitability of the vegetative nervous system. Concomitant is the release of some brake upon the blood pressure mechanisms, so that a family tendency to high blood pressure will flare up. Some women are rendered unstable by the process, others are completely transformed, and still others adapt themselves, with little or no discomfort, to the new situation. The response to the revolution in the cell-republic of the castrate by the other endocrines, the thyroid, the pituitary, and the adrenals, determines which it is to be.