In these studies a constant ERG response was used as a measure of visual sensitivity to different wavelengths of light. The dark-adapted compound eye of Tenodera sinensis is dominated by a single class of photoreceptors. with a major peak of sensitivity at about 510–520 nm, and with a minor peak of sensitivity in the near-ultraviolet region at about 370 nm. The dark-adapted dorsal ocellus does not contain a homogeneous population of sensory receptors. The sensitivity function of the dark-adapted ocellus to longer wavelength light (yellow and red) is determined by a single receptor with a major peak of sensitivity in the green at 510–520 nm with some sensitivity in the near-ultraviolet. Sensitivity at shorter wavelengths (near-ultraviolet and blue), however, involves the stimulation of both this and a near-ultraviolet-sensitive receptor with a maximum sensitivity at about 370 nm. Anatomically, the sensory cells of the dorsal ocellus of Tenodera were determined histologically to be grouped into two distinct regions, each group making its own separate contribution to the ocellar nerve. This may represent the separation of two different photoreceptor types in the ocellus of the mantis.