REACTIONS TO LIGHT. 87 



At 10 a. m. of one day the blinded fishes were removed from the large aquarium 

 and replaced by a number with eyes. These at first remained at the bottom, but on 

 the following morning they were swimming about as the blinded ones had been. 

 The general conclusion from these experiments is that the Chologaster pa pilli ferns 

 with comparatively well-developed eyes can get along without them just as well as 

 with them. 



REACTIONS TO LIGHT. 1 



A long series of observations and experiments was made to determine the reaction 

 of Chologaster and Amblyopsis to white and monochromatic light. Incidentally 

 other characteristics were brought out. 



Some previous experiments on blind or blinded vertebrates may be recalled. 

 Dubois (Compt Rend., t. ex, pp. 358-360) and Semper (p. 79) record that Proteus, the 

 blind salamander of Europe, is sensitive to diffuse light. Graber records that blinded 

 salamanders prefer dark chambers to light ones. Korang (Centralblatt f. Physiol, 

 vi, pp. 3-6) notes that concentrated light deprived of heat rays thrown upon the leg 

 of a frog whose brain had been laid bare and covered with extract of beef, caused 

 it to respond each time with reflex movements. 



That Amblyopsis avoids the light, even the diffuse daylight of a room, is 

 without question. An aquarium was divided in the center by a black partition; 

 one end of the aquarium was covered and the sides painted black, and a small 

 opening was left in one of the lower corners of the partition to enable the fishes to 

 move readily from one chamber to the other. The fishes had no difficulty in find- 

 ing this opening, and at the beginning of the experiment, before the fishes had 

 quieted down from the excitement incident to moving them, they swam back and 

 forth from one chamber to the other as rapidly as it was possible to note the changes. 

 The following are some of the results obtained at separate times: 



Experiment I: Observation on 6 individuals placed in the above aquarium, 

 May 12, 1906, gave, between 9.43 a. m. and 10.20 a. m., 104 events in the dark, and 

 220 in the light. 



This would indicate that the fishes have a preference for the diffuse daylight of 

 the room over that of the dark chamber. But these specimens had been in the 

 light several days, so the light-perceiving or light-reacting organs may have been 

 fatigued. Subsequent events and tables indicate the opposite in such a striking 

 way that the evidenced conclusive. A rapid moving of different individuals 

 from one chamber to another was due to the excitement caused by preparing the 

 aquarium, and the preference shown for one or the other conditions of illumina- 

 tion was entirely overcome by the excitement produced. 



Experiment II : Conditions as in the first experiment with the same 6 individuals 

 in the afternoon of the same day, the aquarium placed so that sunlight entered 

 the lighted end of the aquarium. Result, 114 events in the light, 204 in the dark. 



The second experiment shows that there is an inclination to seek the dark 

 rather than sunlight. That the fishes had not gotten into a normal condition is 

 evidenced by the rapid changes of different individuals from light to dark and 

 vice versa. Toward evening as the direct light was excluded the fishes began to 

 go over to the lighted compartment. 



1 For further studies see Payne, Biol. Bull, xin, pp. 317-323. 



