¹ From the Biological Laboratories, Harvard University, Cambridge, Massachusetts

1. The retinal action potential consists principally of a sustained negative wave which persists for as long as the stimulus. Transitory negative on-effects and off-effects may also be present, particularly at long wave lengths (green, yellow, and red) and in the light-adapted eye.

2. Only the maintained component of the potential can be elicited under CO₂ anesthesia. The transient components are reversibly eliminated from the response at about the same time as the background noise of nerve and muscle spikes. It is suggested that the sustained component arises from the receptor cells, and the other components from second and higher order neurons.

3. The compound eye does not contain a homogeneous population of receptors. A green receptor system (maximum sensitivity at about 535 mµ) determines the response of the dark-adapted eye throughout most of the spectrum; during adaptation to yellow light, however, an ultraviolet receptor system is revealed, with maximum sensitivity at about 345 mµ. The anatomical bases of these receptor systems are unknown; however, they include both retinula cells and neurons in the optic ganglion.

4. There is no change in spectral sensitivity (Purkinje shift) in the first three logarithmic units above the threshold of the retinal action potential.

5. The relatively great effectiveness of near ultraviolet light in stimulating the positive phototaxis of the bee does not depend on excitation of the ultraviolet receptor of the ocellus.

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