. Cave vertebrates of America; a study in degenerative evolution. Cave animals; Evolution. 208 BLIND VERTEBRATES AND THEIR EYES. THE EYES OF LUCIFUGA. The snout of Liici/iiga is broad and depressed to the posterior edge of the max- illaries — duck-bill shaped. The eye is distinguished without difficulty in the trans- lucent living individuals, and even in specimens preserved in formalin or alcohol it is readily distinguished up to very old individuals. In the older specimens the skin over the eye readily discloses the location of the organ. There is over the eye in these specimens a hemiovate
. Cave vertebrates of America; a study in degenerative evolution. Cave animals; Evolution. 208 BLIND VERTEBRATES AND THEIR EYES. THE EYES OF LUCIFUGA. The snout of Liici/iiga is broad and depressed to the posterior edge of the max- illaries — duck-bill shaped. The eye is distinguished without difficulty in the trans- lucent living individuals, and even in specimens preserved in formalin or alcohol it is readily distinguished up to very old individuals. In the older specimens the skin over the eye readily discloses the location of the organ. There is over the eye in these specimens a hemiovate elevation sepa- rated from the rest of the skin of the head by a distinct groove. The skin in this ovate arch is not any less abundantly supplied with pigment than any other part of the head, and there are no other distinguishing features to indicate that it is better adapted to admit light than any other part of the skin of the head. In some cases it is even more densely pigmenterl than neighboring regions. The region is proportionately larger in young individuals than in old, but is more conspicuously de- marked in the older than in the young. Removing the skin shows that beneath the ovate arch lies a mass of orbital fat, approx- imately in the center of which the e3'e lies embedded. The orbital fat-mass seen from above has an oval shape, considerably longer in the of the head than transversely. Behind, the mass touches the orbitaT process of the frontal bone. The eye is y)laccd approximately over the middle of the maxillary. The proportion of the or- bital space or socket occupied by the eye differs greatly in individuals of different sizes. In younger individuals, just about to be born, the eye fills a large part of the socket (plate i6, fig. b), while in the old it forms an insignificant dot in a mass of fat and connective tissue, hundreds of times larger than the eye (plate 2i). The relation of the eye to the surface is similarly conditioned with age. In the young
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