The cerebral cortex, by means of apperceived or reproduced sensual ideas, reacts on the reproductive organs, inducing hyperæmia, secretion of semen, erection, ejaculation. This results by means of centres for vasomotor innervation and ejaculation, which are situated in the lumbar portion of the cord and lie close together. Both are reflex centres. The erection-centre (Goltz, Eckhard) is an intermediate station placed between the brain and the genital apparatus. The nervous paths which connect it with the brain probably run through the pedunculi cerebri and the pons. This centre may be excited by central (psychical and organic) stimuli, by direct irritation of the nerve-tract in the pedunculis cerebri, pons, or cervical portion of the cord, as well as by peripheral irritation of the sensory nerves (penis, clitoris, and annexa). It is not directly subordinated to the will. The excitation of this centre is conveyed to the corpora cavernosa by means of nerves (nervi erigentes—Eckhard) running in the first three sacral nerves. The action of the nervi erigentes, which renders erection possible, is an inhibitory one. They inhibit the ganglionic nervous mechanism in the corpora cavernosa upon the action of which the smooth muscle-fibres of the corpora cavernosa are dependent (Kölliker and Kohlrausch). Under the influence of the action of the nervi erigentes these fibres of the corpora cavernosa become relaxed and their spaces fill with blood. Simultaneously, as a result of the dilatation of the capillary net-work of the corpora cavernosa, pressure is exerted upon the veins of the penis and the return of blood is impeded. This effect is aided by contraction of the bulbo cavernosus and ischio cavernosus muscles, which are inserted by means of an aponeurosis on the dorsal surface of the penis. The erection-centre is under the influence of both exciting and inhibitory innervation arising in the cerebrum. Ideas and sense-perceptions of sexual content have an exciting effect. Also, according to observations made on men that have been hung, it is evident that the erection-centre may be excited by excitation of the tract in the spinal cord. Observations on the insane and those suffering with cerebral disease show that this is also possible as a result of organic irritation in the cerebral cortex (psycho-sexual centre?). Spinal diseases (tabes, especially myelitis) affecting the lumbar portion of the cord, in their earlier stages, may directly excite the erection-centre.