Pseudopupil

Dark spot on the compound eyes of some invertebrates

In the compound eye of invertebrates such as insects and crustaceans, the pseudopupil appears as a dark spot which moves across the eye as the animal is rotated. This occurs because the ommatidia that one observes "head-on" absorb the incident light, while those to one side reflect it. The pseudopupil therefore reveals which ommatidia are aligned with the axis along which the observer is viewing.

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