[B] American Naturalist, 1872, Plate II, Figs. 1 and 2.
[C] Untersuchungen z. Anatomie und Histologie d. Tiere, Plate III, Fig. 28.
[D] American Naturalist, 16, 1882, p. 2.
Aside from the tactile organs in ridges, there are many solitary ones not evident from the surface in Amblyopsis. When the epidermis is removed by maceration, the dermal papillæ on which these rest give the whole head a velvety appearance.
In the young, at least of Amblyopsis, each of the tactile organ of the ridges is provided with a club-shaped filament abruptly pointed near the end. They wave about with the slightest motion in water, and are so numerous as to give the whole head a woolly appearance.
To recapitulate the facts ascertained concerning the eye and tactile organs:
1. The eyes were degenerating and the tactile organs developing beyond the normal before the permanent underground existence began.
2. The eyes continued to degenerate and the tactile organs to increase after permanent entrance to underground waters.
3. In the degeneration of the eye the retina leads; the vitreous body and lens follow; the more passive pigmented layer and sclera remain longest; the bony orbit is not affected.
Bearing of the Facts gained on the Origin of the Cave Fauna.—The origin of the cave fauna and of the blind fauna are two distinct questions. This was first recognized by H. Garman. Before, the two questions were considered as one, and two explanations are prominent among those suggesting its solution: