. Cave vertebrates of America; a study in degenerative evolution. Cave animals; Evolution. 56 BLIND VERTEBRATES AND THEIR EYES. THE EYES OF TYPHLOPS LUMBRICALIS. The eye sliows through the large ocular scale, which entirely covers it. It appears as a black spot surrounded by an unpigmented circle. The preocular, also a large scale, overlaps the ocular and reaches just to the edge of the eye (figs. 20 a, b). Compared with one of the garter /^ as Qs snakes and in proportion to the size - of the head, the eye of Typhlops lum- /^'(^/ifV bricaUs is situated farther from the surfa
. Cave vertebrates of America; a study in degenerative evolution. Cave animals; Evolution. 56 BLIND VERTEBRATES AND THEIR EYES. THE EYES OF TYPHLOPS LUMBRICALIS. The eye sliows through the large ocular scale, which entirely covers it. It appears as a black spot surrounded by an unpigmented circle. The preocular, also a large scale, overlaps the ocular and reaches just to the edge of the eye (figs. 20 a, b). Compared with one of the garter /^ as Qs snakes and in proportion to the size - of the head, the eye of Typhlops lum- /^'(^/ifV bricaUs is situated farther from the surface and occupies far less space, while Harder's gland, associated with the e)'e in both, is relatively much larger in Typhlops. In a specimen of Fig. 20. (3) Dorsal View of Head of r^'M/ofs. 21 tm. long TvpJilops IIIjubriculIS 21 cm. in length, (/i) Lateral View of Head of same Specimen. a i o ^ the eye measured mm. in width, and mm. in depth. The greatest width of the gland of the same was mm. and the length was mm. The gland completely surrounds the eye up to the edges of the conjunctival sac (plate 4, figs, a, b). In proportion to the size of the eyes, the gland of the garter snake is much smaller than that of Typhlops lumbricalis, but compared with Rhinciira Jloridana the gland of Typhlops Iwnbricalis is but little more than half as large. The eye is covered by layers of epidermis and dermis that differ from these same layers on neighboring parts by being thinner, more compact, and free from pigment and glands. The ocular scale, however, which covers the eye region, docs not differ in thickness from the other scales of the head (plate 4, fig. a). A conjuncti\'aI sac is present with a diameter at least as great as the greatest width of the eye bulb. The conjunctiva, which forms this sac, is very thin over the cornea and next to the l)rille, where it measures ^"''- ^t the edge of the sac it is diflerentiated into glands, the fornix conjunctiv
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