. Cave vertebrates of America; a study in degenerative evolution. Cave animals; Heteropygii. 132 BLIND VERTEBRATES AND THEIR EYES. will suggest the homology of the anterior cell mass in the latter case, with the pig- ment cells always present between the retina and the irideal pigment layer in the former species. This correspondence is further strengthened by the fact that frequently the pigment in T. rosa over the front of the eye is in more than one layer of cells. Since, however, I was unable to arrive at an entirely satis- factory explanation of the origin of this pigment mass in Amblyopsi
. Cave vertebrates of America; a study in degenerative evolution. Cave animals; Heteropygii. 132 BLIND VERTEBRATES AND THEIR EYES. will suggest the homology of the anterior cell mass in the latter case, with the pig- ment cells always present between the retina and the irideal pigment layer in the former species. This correspondence is further strengthened by the fact that frequently the pigment in T. rosa over the front of the eye is in more than one layer of cells. Since, however, I was unable to arrive at an entirely satis- factory explanation of the origin of this pigment mass in Amblyopsis, it will not help us much, should the two structures be homologous. Attention may be called here to the fact that both in Amblyopsis and in the pres- ent species the lens — and therefore the lost pupil — are not situated at the distal pole of the eye, but above this point, and that both in regard to the pupil and the eye in general the location of the pigment masses in the two species is the same. The pigment is granular, ,iot prismatic. scl. c. Fig. 48. Cross-sections through Right and Left Eye of an Individual 25 mm. long. Sections be pass through Lens. Fig. a is a Composite from 3 Sections. Fig. b represents one Section, but the '* Lens " is from the Next Section. The lens is the only structure of the eye concerning which Kohl has not made any It is a small group of cells closely crowded together and about 10 or 12 fj. in diameter (figs. 48 a' and b, I). There are no signs of fibrilation or the result of any other histogenic process; it appears as an aggregation of indifferent cells. On its surface there are at times cells that are evidently of an epithelial nature, being flattened so that their sections appear much longer than deep. It lies at the upper outer face of the eye at the margin of the pigment mass described in the last section. It is not covered by pigment or other retinal substance. Kohl considered this condition a primary one. The lens, how
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