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Abstract
Electron microscopy suggests that the squirrel retina has two types of receptors whose outer segments possess rodlike and conelike structural details, respectively. They are further distinguished by the length and diameter of their outer segments and by the shapes and location of their nuclei. Increased membrane density is noted at contact points between the pedicle plasma membranes of the receptors and suggests interreceptor synapses. These have been noted between cells possessing rodlike and conelike outer segments and between cells with similar outer segments. On one occasion such a contact patch appeared to involve a glial and a receptor cell. Questions are raised relative to the identification and definition of receptors as rods or cones, the interpretation of "all cone" electroretinograms, as well as the visual pigment content of this retina. The problem of the retinal attachment mechanism is considered. Other receptor regions are also described.