. Cave vertebrates of America; a study in degenerative evolution. Cave animals; Evolution. THE TACTILE ORGANS. 97 as in the other species. In Chologaster cormitus there are no distinct ridges at all, the tactile organs being arranged as in other species of fishes. In specimens of the same size the papillae are not more prominent in papilUferus than in cornutus. It is only in the oldest of papilliferns that the papillae become prominent. The number of individual papilke in each tactile ridge differs considerably with age (size), so that an exact comparison between the large Amblyopsis and the m
. Cave vertebrates of America; a study in degenerative evolution. Cave animals; Evolution. THE TACTILE ORGANS. 97 as in the other species. In Chologaster cormitus there are no distinct ridges at all, the tactile organs being arranged as in other species of fishes. In specimens of the same size the papillae are not more prominent in papilUferus than in cornutus. It is only in the oldest of papilliferns that the papillae become prominent. The number of individual papilke in each tactile ridge differs considerably with age (size), so that an exact comparison between the large Amblyopsis and the much smaller species of Chologaster and Typhlichthys can not be made. From a num- ber of counts. Professor Cox found that ridge No. 6 contains in Chologaster papilU- ferus, 6 organs; in Typhlichthys, ii; in two specimens of Amblyopsis, respectively and inches long, 12 and 20. The tactile ridges in the head of Amblyopsis. 2. (a,b,c) Distribution of Tactile Ridges in .4mi/yo^i/j; lateral, dorsal, and ventral views. (rf, e) Distribution of T-actile Ridfies in Typhlichthys iubterraneus; dorsal and side views. are shown in plate 8, figures A and b. The outermost layer of skin has been re- moved from a small area over the right eye of A, showing the numerous taste buds. Figures c and d show head of Chologaster papilUferus under slightly greater mag- nification. Figure D shows especially the tactile organs about the mouth. The skin passes over the eye without a free orbital rim, and the eye does not show well. Aside from the tactile organs in ridges there are many solitary ones not evi- dent from the surface in Amblyopsis. When the epidermis is removed by macera- tion, the dermal papillae on which they rest give the whole head a velvety appearance. In the young, at least, of Amblyopsis, each of the tactile organs of the ridges is provided with a club-shaped filament abruptly pointed at the end (fig. 31). They wave about with the slightest motion in water and are so numerous a
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