THE optic glands of Octopus vulgaris lie on either side of the central part of the supraoesophageal brain, on the stalks of the optic lobes (Fig. 1): they control hormonally the onset of sexual maturity in female octopuses1. Production of hormone is regulated by an inhibitory nerve supply from the subpedunculate lobe. This in turn is probably affected by daylength, for section of optic nerves causes precocious sexual maturity in octopuses1, and a period of artificially reduced daylength can accelerate the normal onset of sexual maturity in Sepia2. A single optic gland hormone apparently determines the state of maturation of both ovaries and oviducts3.