POLARIZED LIGHT AND ANGLE OF STIMULUS INCIDENCE IN THE COMPOUND EYE OF LIMULUS

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Abstract
To test the effect of the incident angle of the stimulus on single ommatidia of the Limulus eye using polarized light, an adjustable Polaroid filter was placed between a depolarizer and the shutter of the optical system. When an electrophysiologically single element of the optic nerve showed marked sensitivity to the plane of polarization of the light illuminating the corresponding om-matidium, with continuous illumination the frequency of optic-nerve impulses varied systematically with the plane of polarization passing through maxima and minima 90[degree] apart. With flashes of light, different numbers of action potentials resulted from exposures of the same intensity and duration but of different planes of polarization, with maxima and minima 90[degree] apart. It was previously found that rotation of the eye into a new orientation relative to the stimulus could affect the difference between the maximal and minimal points. Use of ommatidia with optical axes normal to the corneal surface obtained by restricting the excitable elements to the central region of the eye with opaque paint, showed that when the stimulus entered an ommatidium parallel to its optic axis and normal to the corneal surface, little or no polarized-light sensitivity was shown in the responses with respect to flashes. When the stimulus had a large incident angle to the ommatidial axis, there was evidence that the ommatidium could analyze polarized light. Results are discussed in connection with work on other arthropod eyes.

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