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To recapitulate, the at present accepted theory concerning the mechanism controlling the menstrual cycle is, that it is governed by the anterior lobe, which probably produces two hormones: (1) Prolan A, which stimulates follicular maturation in the ovary, and the secretion of oestrone, which in turn causes the endometrium to develop to the post-menstrual phase, and. (2) Prolan B, which causes the formation of the corpus luteum and the secretion of Progesterone, which advances the development of the endometrium to that of the pre-menstrual phase. The pituitary then might be termed the conductor of the instruments of the menstrual orchestra, directing its harmony, but, from what score must the conductor beat the tempo? What music is to be played? In plainer terms, is there a higher nervous sexual centre, which controls the hormone function of the ipituitary? Hohlweg and Junkmann have suggested by their experiments on castrated rats, into which implants of hypophyseal tissue have been made, that the pituitary is controlled extrinsically by fine nerve connections to the brain via the pituitary stalk. Theobald has recently put forward an hypothesis from evidence of a clinical nature, which postulates that there are one or more centres in the brain, probably in the hypothalmic region, which regulate the functions of the reproductive tract, through afferent and efferent neuro-hormonic stimuli. He considers the efferent route to be composed by: (1) The hormones of the anterior lobe, and (2) Nervous impulses to the generative organs; and the afferent pathway to be composed of: (1) The hormones of the ovary. (2) Impulses transmitted from the external generative organ. (3) Impulses transmitted from the higher special centres. This hypothesis is rather novel and attractive, yet it requires the corroboration of more fundamental study. It, however, causes a swing of the pendulum in the opposite direction, in focussing the attention of investigators of this subject, to a higher centre or centres, which may be the final link in the chain whereby the phenomena of menstruation, ovulation, pregnancy and parturition can be more adequately explained.