THE BLIND FISHES OF NORTH AMERICA.
By CARL H. EIGENMANN,
PROFESSOR OF ZOÖLOGY, INDIANA UNIVERSITY.
“An investigation into the history of degenerate forms often teaches us more of the causes of change in organic Nature than can be learned by the study of the progressive ones.”—Weismann.
The caves of the United States are inhabited by three cave salamanders, two of them with degenerate eyes; by six cave fishes, all with impaired vision—five of them with rudimentary eyes, one with eyes the most degenerate among vertebrates; and by several mammals. It is thus seen that among the interesting features of the North American fauna the blind vertebrates are not the least. Yet during the past twenty-five years the only additions to our knowledge, aside from diagnoses of new species, have been a few random notes on the habits and a short account of the eye of Troglichthys by Kohl.
Various classes of vertebrates have blind members, but no large vertebrate has become blind or permanently taken up its home in caves. Blatchley reports that a number of cats have established themselves in Wyandotte Cave, where they bring forth and rear their young. They have exterminated the cave rats, and now station themselves in a narrow passage of the cave and capture bats as they fly through.
Among the permanent residents in dark places we have, among mammals, the moles, which habitually live in burrows of their own make. In Mammoth Cave lives a rat—Neotoma pennsylvanica. In Marengo Cave, Indiana, white-footed mice have established themselves. Although with unimpaired eyes, they have acquired ears and whiskers longer than the rest of their kind living outside.
In Florida occurs a blind lizard—Rhineura floridana. It burrows in the ground, and is colorless and blind.
Fig. 1.—The cave salamander of the Mississippi Valley
(Spelerpes maculicauda).
Of salamanders, one blind species lives in European caves. In the large caves of the eastern United States no blind salamanders have been found, although other species, especially Spelerpes maculicauda, abound. In the caves of Missouri a veiled-eyed salamander, Typhlotriton, has been described within recent years by Stejneger. Still another salamander, Typhlomolge, having rudimentary eyes, has been cast up from an artesian well at San Marcos, Texas, and occurs in the cave streams about that place.
The most abundant of the blind vertebrates, both in individuals and in species, are the blind fishes. These, from their geographical distribution, may be separated into three groups: (1) Those inhabiting the depths of the ocean; (2) those inhabiting dark places along the shores of the ocean; (3) those inhabiting the underground fresh waters.