Summary
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1.
The external plexiform layer of the retina was examined in the frog (Rana temporaria), the chick (Gallus domesticus), the tortoise (Testudo graeca), and the rabbit, guinea pig, cat and bush baby in order to compare differences of morphology and concentration per unit area between rod vesicles and cone vesicles.
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2.
Rod synaptic vesicles were observed to differ consistently from cone synaptic vesicles in size, shape, electron density and concentration per unit area.
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3.
Counts were made in the frog retina of the ratio of rod vesicle concentration per unit area to cone vesicle concentration per unit area, using those pictures where rod endings and cone endings were shown on the same electron micrograph.
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4.
In the cone endings in frog, chick and tortoise synaptic vesicles around the presynaptic membrane were observed to be of the “complex” variety. “Complex” vesicles were also observed in relation to paired presynaptic membranes in synaptic diverticula in chick and tortoise cone endings. Their possible significance with reference to the origin of synaptic vesicles is discussed.
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5.
Some peculiarities of morphology of the visual cell synaptic area in chick rods and tortoise cones are reported.
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6.
Small polarised contacts are described in the frog, chick and tortoise retinae, occuring between the invaginating dendrites and the receptor cell with a bipolar-to-receptor polarisation.
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I am indebted to Prof. J.Z. Young and Dr. E.G. Gray for advice and encouragement, and to Mr. S. Waterman for photography.
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Evans, E.M. On the ultrastructure of the synaptic region of visual receptors in certain vertebrates. Zeitschrift für Zellforschung 71, 499–516 (1966). https://doi.org/10.1007/BF00349610
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DOI: https://doi.org/10.1007/BF00349610