Page:Popular Science Monthly Volume 56.djvu/491

Rh method of locating and securing food which has enabled the Amblyopsidæ to establish themselves in caves.

The Chologaster in general make-up is like Amblyopsis, but is somewhat longer-jointed. It sits with its pectorals extended. When it moves horizontally for some distance the pectorals are usually pressed to the sides, the propelling being done largely by the tail very much after the manner of a salamander, which it resembles. In swimming toward the surface it uses its pectoral fins chiefly, and the fish usually sinks to the bottom as soon as its efforts to raise itself are stopped.

Individuals kept in aquaria with one end darkened either collected in the darkened area floating about, or under leaves or sticks in any part of the aquarium. They are frequently found under a floating board, where they float with the tops of their heads in contact with the board, their bodies slanting downward. They seek the dark, regardless of the direction of the rays of light. These characteristics they have, in great part, in common with the blind members of the family. The adult Amblyopsis frequently floats with its head to the top of the water, the tail sloping downward, and in swimming along ledges of rock the top of the head is applied to the ledge. I have captured many specimens simply by scraping my net along the surface of a ledge.

Typhlichthys, living in total darkness, has retained the habit of staying under floating boards, sticks, and stones. Miss Hoppin noticed that Troglichthys swims with its back to the sides of the aquarium, and I have repeatedly noted the same in the young of Amblyopsis up to fifty millimetres, and the still younger Amblyopsis frequently hides under rocks.

—The general impression given by Amblyopsis is that of a skinned catfish swimming on its back. The expressions, "They are catfish"; "They look as though they were skinned"; "They are swimming on their backs," are heard from those who see these fishes for the first time.

The largest individual secured by me measured 135 millimetres in total length. Individuals as large as this are rare. The usual length of an adult is about 90 millimetres. One individual was mentioned to me at Mammoth Cave having a length of 200 millimetres!

Amblyopsis is found in pools in the cave streams it inhabits. I have secured as many as twelve from a pool perhaps ten by fifty feet in size. Very rarely they are to be found in the riffles connecting the pools. I have seen them lying at the bottom, or swimming, or rather gliding, through the water like "white aquatic ghosts." In the aquarium they lie at the bottom or at various depths in the