Page:Popular Science Monthly Volume 57.djvu/64

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54
THE POPULAR SCIENCE MONTHLY.

papilliferus most of the ridges are much less prominent than in the blind species, being sunk into the skin. About the nose and chin, however, the ridges are as prominent as in the other species. In the small Chologaster cornutus there are no distinct ridges

PSM V57 D064 Chologaster papilliferus with the tactile ridges.png
Fig. 6.—Snout of Chologaster papilliferus to show the tactile ridges.

at all, the tactile organs being arranged as in other species of fishes. In specimens of the same size the papillæ are not more prominent in papilliferus than in cornutus. It is only in the oldest of papilliferus that the papillæ become prominent. The number of individual papillae 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 number of counts made by Professor Cox I take the liberty of giving the following: Ridge No. 6 contains, in Chologaster papilliferus, six organs; in Typhlichthys, eleven; in two specimens of Amblyopsis, respectively eighty-three and one hundred and six inches long, twelve and twenty.

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,