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"Degeneration," says Lankester, "may be defined as the gradual change of the structure in which the organism becomes adapted to less varied and lesis complex conditions of life; whilst elaboration is a gradual change of sti-ucture in which the organism becomes adapted to more and more varied and complex conditions of existence." Degeneration may affect the organism as a whole or some one part. I propose to speak not on degeneration in general but to give a concrete example of the degeneration of the parts of one organ. The eyes of the blind vei-tebrates of North America lend themselves to this study admirably, because different ones have reached different stages in the process, so by studying them all we get a series of steps through which the most degenerate has passed, and ai^e enabled to reach conclusions that the study of an exti-eme case of degeneration would not give us. I shall confine myself to the cave salamanders and the blind fishes (Amblyopsidae) nearly aU of which I have visited in their native haunts. The salamandea-s are introduced to illuminate some dark points in the degeneration of the eyes of the fishes and to emphasize a fact that is forcing itself forward with increasing vehemence; i. e., that cross-country conclusions are not warrantable; that the blind fishes form one group and the salamanders other groups, and that however much one may help us to understand the olher, we must not expect too close an agreement in the steps of their degeneration under similar conditions. Thei-e are three cave salamanders in North America.

Degeneration in the Eyes of the Coldblooded Vertebrates of the North American Caves