﻿REACTIONS TO LIGHT. 89 



ently to find their way out. After a day, however, all had collected in the dark 

 chamber and it was rare that any of them came out into the light chamber. They 

 remained in the dark chamber for days without coming out, except occasionally 

 at night. On May 24 the blind fishes remained in the dark compartment until 

 night, when all collected in the light compartment, only to be found back again 

 in the dark the next morning. 



Everything indicates that they readily perceive light, even the diffuse light of 

 a room, and that they individually react negatively to light. 



Four Amblyopsis which had been kept for a day in a vessel painted black and 

 covered to exclude the light were experimented upon as follows: a ray of light 

 from a microscope mirror about 2 inches in diameter was thrown on each success- 

 ively. After from i to 5 seconds the fishes became uneasy, the uneasiness giving 

 place to discomfort, the fishes making vigorous efforts to get out of the ray. 



Another jar, not painted, containing both Amblyopsis and blind Cambarus, 

 was placed where light could be reflected upon them from the mirror of a micro- 

 scope. The Cambarus, if in motion, came suddenly to a halt ; if quiet, it backed or 

 moved off at once. The fishes also responded to the light but it took several times 

 as long for them to do so. 



Bright sunlight appears to be irritating ; if exposed to it, the fishes swim about 

 uneasily. A shadow passed suddenly across them when in the diffuse light of a room 

 does not affect them, nor do they, when swimming, seem disturbed by a ray of Hght 

 entering the dark chamber through a small hole in the paint made for the experiment. 



Two examples kept in a pail in my cellar were quietly floating, but when a lighted 

 match was held above them the fishes at once darted to the bottom and sides of 

 the pail. The heat could not have been a factor in this case ; the reaction to the 

 light of the match was quick and violent. 



A similar observation was made on 40 individuals in two aquaria. They were 

 captured one morning, and the observation made the second night after. They 

 had been kept in the dark during most of the intervening time. A lighted match, 

 held near the aquaria, produced a very general and active movement among all the 

 individuals. 



Even more striking than this was the action of a colony of Amblyopsis in an 

 open pool. During the bright part of the day the fishes remained under the rocks 

 at the bottom. Occasionally a nose could be seen poking out from under a rock ; 

 perhaps one of the fishes came out at times during the day. In the morning and 

 evening and at night, they could be seen swimming in various parts of the pool. 



The following experiments make it evident that the direction of the light does 

 not influence the actions of these fishes, but that their behavior is due to a per- 

 ception of difference in the intensity of light. A large box, covered at its southern 

 end, was sunk into the ground where the water of a spring flowed through it. 

 Throughout the lighter parts of the day the fishes stayed in the shade of the south- 

 ern part of the aquarium. It was only in the evening, in the morning, and at night 

 that the fishes ventured forth. A similar box 2x4x8 feet, divided in the middle 

 by a partition running to near the bottom, had lids hinged so that either or both 

 compartments could be covered and darkened. Within a short time after one of 

 the compartments was darkened all of the individuals would be found in the dark- 

 ened compartment, irrespective of the direction of the sun's rays. 



