80 BUND VERTEBRATES AND THEIR EYES. 



such an instance. But in this species the bleached condition has not yet been 

 hereditarily established, and since each individual is independently affected, "the 

 main cause of change must have been of that direct order which we understand by 

 the term climatic." 



Since, however, the bleached condition, which in the first instance is an individual 

 reaction to the absence of light, has become hereditarily established in Amblyopsis 

 so that the bleaching goes on even when the young are reared in the light, it is evi- 

 dent that in Amblyopsis we have the direct effect of the environment on the individual 

 hereditarily established. 



GENERAL HABITS OF AMBLYOPSIS. 



The general impression given by Amblyopsis is that of a skinned cat-fish swim- 

 ming on its back. The largest individual secured by me measured 135 mm. in 

 total length. Individuals as large as this are rare. The usual length of an adult 

 is about 90 mm. At Mammoth Cave I was told of an individual having a length 

 of 200 mm. 



Amblyopsis is found in pools in the cave streams it inhabits. I have secured 

 as many as 12 from a pool perhaps 10 by 50 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, rather gliding, through the water like "white aquatic ghosts." In 

 the aquarium they lie at the bottom or at various depths in the water, their axes 

 making various angles with the horizontal, their pectorals folded to their sides. 

 When swimming slowly, it is chiefly by the use of the pectorals. The strokes of 

 the pectoral are lazily given, and the fish glides on after a stroke till its impetus is 

 exhausted, when another stroke is delivered. The fishes frequently roll slightly from 

 side to side at the exhaustion of the result of a stroke. When swimming rapidly, 

 the pectorals are folded to the sides and the locomotion is then similar to that of 

 a salamander, by the motion of the tail. They readily adjust themselves to differ- 

 ent depths and are usually perfect philosophers, quiet, dignified, unconcerned, and 

 unperturbed, entirely different from such eyed species as minnows and sun-fishes, 

 which are sometimes found in caves, and which are much more readily disturbed by 

 any motion in the water, making it almost impossible to capture them. The pec- 

 torals are also almost exclusively used when quietly rising in the water. At such 

 times the pectorals are extended laterally and then pressed to the sides, beginning 

 with the upper rays. A downward stroke is delivered in this way, not quickly, but 

 with apparent lazy deliberation. In swimming forward the pectorals are brought 

 forward, upper edge foremost. The center of gravity seems to be so placed in 

 regard to their various axes that the fish does not lose its balance whatever its posi- 

 tion. It floats horizontally in the water without any apparent effort to maintain 

 its position. It floats with the main axis inclined upward, with the snout some- 

 times touching the surface of the water, apparently lifeless. Once one was seen 

 resting on its tail in a nearly vertical position, and one while quietly swimming 

 leisurely turned a somersault and swam on undisturbed. At another time the 

 same individual rolled completely over. When one is kept out of water for a short 

 time, it frequently goes in a corkscrew-shaped path through the water, continually 

 spinning around its long axis. In their quiet floating position it is difficult to deter- 

 mine whether they are alive or not. 



