The focal lengths, radii of curvature and refractive indices of the lenses of the principal and side eyes have been measured. In layer 4 they are ovoid, and are oriented approximately at right angles to the light.Īt the first optic glomerulus the primary fibres from each receptor layer appear to terminate in separate regions of neuropile. In layers 1, 2 and 3 the rhabdomere-containing segments are rod-shaped, and are parallel to the incident light. The more superficial layers (3 and 4) are confined to the central region of the retina. The minimum receptor separation is 1.7 μm., or 11 min. The deepest layers (1 and 2) cover the whole area of the retina, and have the greatest density of receptors. The distribution of receptors in each layer has been determined. The retinae of the principal (AM) eyes of jumping spiders contain four layers of receptors, one behind the other with respect to the incident light.
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