Insect pupil mechanisms
The pupil mechanism of Hymenoptera (suborder Apocrita) has been studied by simultaneous recordings of transmission and reflection from the compound eye of virtually intact animals. It is confirmed that the light flux in the photoreceptors is controlled by pigment granules in the retinula cells; the pigment migration serves a pupil function. Experimental methods are described for investigation of the pupil process using only reflection measurements. Using polarised light, it is found that backscattered light from the rhabdom is more strongly depolarised than light backscattered from retinula cell pigment granules.
The dynamic characteristics of the pigment migration are determined more accurately than could be done previously with histological methods (Menzel, 1972a, b; Kolb and Autrum, 1972, 1974). The hymenopteran pupil mechanism has a familiar sigmoid intensity dependence; the time constant is 5–15 s. The pupil absorbance spectrum is broad, peaking at about 520 nm. The correspondence of this spectrum with known spectral sensitivities exemplifies that the pupil mechanism is a useful part of the visual system.
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