MORPHOLOGY OF THE OMMATIDIA OF THE COMPOUND EYE OF LIMULUS

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Abstract
The sensory portion of the ommatidium of the compound eye of Limulus, and the sensory portion of the eye of Scutigera, and of the spider were studied with the electron microscope. In axial longitudinal section the Limulus rhabdom appears to be made up of small polygons, and in transverse section the rhabdom appears as a banded structure of dark lines. Thus in three dimensions the rhabdom resembles a honeycomb composed of tubular units, the long axes of which lie in transverse planes and are oriented perpendicular to the retinula cell''s contours. The rhabdom''s tubular units, which are about 140 m[mu] in diameter in Limulus and 70 m[mu] in diameter in the spider and Scutigera, are microvilli of the borders of the receptor cells. The walls of these microvilli are continuous with fine linear structures (membranes) in the cytoplasm of the receptor cells. In transverse sections of the Limulus ommatidium, oval bodies interpreted as mitochondria are observed in an annular zone at the tips of the rhabdom''s rays. These mitochondria, which are 2 - 10 [mu] in diameter, are crowded with irregular closed outlines about 100 m[mu] in diameter. Possible functions of components of the Limulus ommatidium are discussed.

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