. Cave vertebrates of America; a study in degenerative evolution. Cave animals; Evolution. 114 BLIND VERTEBRATES AND THEIR EYES. â 0 â ".. '.Si-a m. Q^S3 2- OOP Oo 0^ 6 000^ ^ 889 C layer exclusive of the twin cone nuclei. But extending just with- out the external limiting membrane a large number of short processes are seen between the cone nuclei (fig. 35 c). Whether these are degenerate rods, I am unable to say. The outer nuclear layer differs materially in the younger, , smaller (29 mm.), specimens and in the largest specimens. In the younger specimens it consists of several layers
. Cave vertebrates of America; a study in degenerative evolution. Cave animals; Evolution. 114 BLIND VERTEBRATES AND THEIR EYES. â 0 â ".. '.Si-a m. Q^S3 2- OOP Oo 0^ 6 000^ ^ 889 C layer exclusive of the twin cone nuclei. But extending just with- out the external limiting membrane a large number of short processes are seen between the cone nuclei (fig. 35 c). Whether these are degenerate rods, I am unable to say. The outer nuclear layer differs materially in the younger, , smaller (29 mm.), specimens and in the largest specimens. In the younger specimens it consists of several layers of cells exclusive of the cone cells, which in this case can be counted with the laver of rods and cones. In the larger specimens this is reduced to a single layer of nuclei less densely packed, with occasionally a horizontal nucleus near the base which is less granular, staining a more uni- form color. In the largest specimen the outer nuclear layer makes up about 7 per cent of the total thickness of the retina, in the smaller specimens it is slightly thicker, forming 10 per cent of the total thickness. The outer granular layer differs also materially in the largest and smallest specimens. In the largest it forms a thin layer entirely free from nuclei and with a total thickness of but 2 or 3 /x. In a specimen 39 mm. long this layer is 5 /x thick, distinctly granular, contains a few round nuclei â not differing from those of the inner nuclear layer. (See fig. 35 c.) These are probably members of the layer of fulcrum cells. The latter are not separable from the underlying bipolar cells in other regions. In tangential sections they appear in groups of two, but are much fewer in number than the twin cone cell. The inner layer of the inner nuclear layer is composed of distinctly larger cells in the largest specimen and separated from the rest by a slight interval. The 8o-o:-oo^-. â â «.rjr» 6; â â¢â .â¢-â¦. Please note that these images are extracted from scanne
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