COLOR CHANGES AND ADAPTATION IN FISHES. 



213 



some tests a black cork containing two small holes was inserted in the bottom of the 

 tube. These holes were of such a size and were so located that the two beams of light 

 passing through just covered the two eyes. 



In all of the tests the light received by the eyes from above, compared with that 

 received from the background, was 



'-- V'-" 



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1 



abnormally intense ; and in accord with 

 the hypothesis under consideration the 

 fish should have become abnormally 

 dark. This, however, did not occur. 

 In most of the tests the fish was allowed 

 to become maximum white in the 

 cylinder in low light intensity before 

 the eyes were illuminated from above; 

 but in other tests a piece of black cloth 

 was put under the crystallizing dish 

 and the fish was allowed to become 

 maximum black; then the cloth was 

 removed from imder the dish and the 

 light from the tube turned on. In 

 still other tests a piece of bristol board 

 containing black and white 5 mm, 

 squares was put under the glass dish 

 and the fish was allowed to become 

 mottled before turning on the light 

 through the tube. Without going 

 further into details, the results may be 

 summed up by saying that the increase 

 in illumination from above induced no 

 observable change, although the beam 

 of light was directed on the eyes, in 

 some instances, continuously for over 

 two hours, a period much longer than 

 was necessary for a complete change 

 in this individual from black to white 

 or vice versa. 



At first thought, these results ap- 

 pear to contradict the idea that the 

 shade assumed by the fish depends 

 upon the ratio between direct and re- 

 flected light. The fact, however, that in all of these tests the fish retained the shade 

 it had at the beginning of the increase in illumination from above, no matter whether it 

 was dark or light or mottled, indicates merely that under the conditions of the experiment 

 the chromatophores did not respond at all. The excessive illumination of the eyes 

 from above entirely prevented stimulation by light reflected from the white back- 



FlGl 3. — Vertical section of apparatus used in testing, in flounders, 

 the effect of abnormally increasing tlie relative amount of light 

 received by the eyes from above. A, aquarium; CD, crystallizing 

 dish; S, siphon; I, inlet for water; O, outlet; C, opaque cylinder; 

 T, iron tube; M, mirror; L, small beam of light. 



