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Abstract:
Exner's theory of the formation of a retinal image by superposition1 in certain arthropod compound eyes requires that an object in front of a number of ommatidia is twice inverted by the dioptric system of each ommatidium. Thus erect images of the object are formed behind the crystalline cones. Converging proximally, those images grow in size and superimpose in the layer of the receptive structures, the rhabdoms. Exner tested his theory by observing the image formation in sectioned eyes and found agreement between experiment and theory in more than a dozen insect species. His findings were confirmed repeatedly using the firefly2–4. (Although Exner proposed the formation of superposition images in certain Crustacean eyes, he failed to obtain upright and superposition images. So did other observers2,3. Crustacea will therefore be excluded.)
