The production or emission of light is under nervous control in many marine animals that have a differentiated nervous system. The nature of this control is a field of neuro-effector physiology that has been little explored, but one which could advance considerably our knowledge of the behaviour and functioning of luminescent marine animals. Nervous control of luminescence is achieved in diverse ways in different animals, namely, by squeezing forth a pre-formed secretion through muscular contraction, as appears to take place in Cypridina; by exposing a continuously luminescent organ through rotation or by movement of shutters, as in the teleosts Photoblepharon and Anomalops; by initiating cellular changes that lead to intracellular luminescence, for example in the photophores of the shrimp Acanthephyra debilis; and by directly activating light gland cells to secrete. The last method is a special example of nervous regulation of glandular secretion, and is the process occurring in the polychaete Chaetopterus (Dahlgren, 1916; Harvey, 1920, 1940).