A Metasomatic Neural Photoreceptor in the Scorpion

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Abstract
There are extraocular photoreceptors in the metasoma of different species of the scorpion Heterometrus (H. fulvipes var. I, H. fulvipes var. II and H. gravimanus).The relative sensitivity of the different parts of the metasoma differs in the different species of Heterometrus studied.The telsonic nerves, although sensitive to light, are not solely responsible for the extraocular perception of light, and cutting of the telsonic nerves does not abolish the response in any of the species of Heterometrus used.With increase in the intensity of light stimulus the latency of response decreases and the impulse frequency increases in the responding units; and a greater number of units are excited.With prolonged exposure of the receptors to light some units become adapted, and the rate of adaptation is different in the telsonic response as compared to the ganglionic response in H. gravimanus.Spectral sensitivity is the same in the different species of Heterometrus tested, and the peak response is obtained at 568 nm with a smaller peak at 440 nm.