Oxygen-sensitive elements in the book gills of Limulus polyphemus

The unit responses of oxygen-sensitive elements in the book-gill lamellae of Limulus polyphemus were examined by recording their unit activities in the gill nerve while varying the oxygen tension in the sea water bathing the lamellae. Three types of oxygen-sensitive units were detected. Some units (class I) were excited by oxygen introduced into anaerobic sea water; others (class II) were inhibited by high oxygen levels. Some units responded to tactile stimulation only in the presence of oxygen. It is suggested that the oxygen-dependent ventilatory reflexes result from interaction in the central ventilatory neural system of the excitatory effects of class I units and of touch-sensitive oxygen-dependent units with the inhibitory effects of class II units.