. Cave vertebrates of America; a study in degenerative evolution. Cave animals; Evolution. EYES OF THE TEXAN CAVE SALAMANDER. 33 THE PIGMENT LAYER, EXCLUSIVE OF THE IRIDEAL PARTS. The pigment layer is a thin, compact layer, densely pigmented. In an indi- vidual 30 mm. long it is abont8/ti in thickness. As there are no rods and cones, the inner surface of this layer is similar to the outer, that is, the cells form a pave-. n. op. â I I Fig. 5. (u) Right Eye of Specimen of Ty/'Wf'Hw/^f 30 ram. Ion;;. (/») Exit of Optic Nerve of Same, (f) Iris of Left Eye of Specimen, (d) Upper Half of Iri
. Cave vertebrates of America; a study in degenerative evolution. Cave animals; Evolution. EYES OF THE TEXAN CAVE SALAMANDER. 33 THE PIGMENT LAYER, EXCLUSIVE OF THE IRIDEAL PARTS. The pigment layer is a thin, compact layer, densely pigmented. In an indi- vidual 30 mm. long it is abont8/ti in thickness. As there are no rods and cones, the inner surface of this layer is similar to the outer, that is, the cells form a pave-. n. op. â I I Fig. 5. (u) Right Eye of Specimen of Ty/'Wf'Hw/^f 30 ram. Ion;;. (/») Exit of Optic Nerve of Same, (f) Iris of Left Eye of Specimen, (d) Upper Half of Iris of Right Eye of Specimen of Typhlomolge 70 mm. long. ment epithelium. In places, however, processes of the cells extend in among the cells of the nuclear layers, for a distance of 40/^ in some cases (fig. 5a), to the inner reticular layer. In the individuals 70 to 90 mm. long, the pigment epithelium reaches 16 /a in thickness. The only indication of a lens wras found in the eye of a specimen 72 mm. long. In this a small lenticular group of cells lay in the opening of the pupil. It measured 24 x 40/a (fig. 6). i 1-- THE IRIS AND ORA SERRATA. Marked changes take place in the iris from the smallest to the largest individuals examined, so that these must be dealt with seriatim. The smallest individual is 30 mm. long (fig. 5 a and c). On the left side the pupil measures 22 /a in diameter; the distance from the margin of the pupil to the ora serrata measures approximately 100/x,. The epithelial part of this iris consists of an outer layer of dense pigment considerably (14/^) thicker than the pigment epithelium of the rest of the eye. At the pupil this pigment appears rolled into the inner surface of the iris, where it is continuous with the inner layer of cells, which consists of a layer of ordinary pigmentless epithelium 6 fi thick, with the nuclei elongate and placed obliquely, and 24/a in length. A few of these ordinarily pig- mentless cells show pigment. There is a distinct
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