EXPERIMENTS ON COLOUR-CHANQE IN TENCH. 839 



5. Both fishes were now put back into the dark aquarium 3, 

 and on the following morning (April 9th) both were of the deep 

 green colour. 



I thought that the above-described experiments deserved to 

 be recorded because, though not perhaps of an original nature, 

 and relating to only two individuals, they were of themselves 

 sufficiently definite to allow of certain conclusions being drawn, 

 and might therefore be acceptable as additional evidence that 

 the Tench can, to a certain extent, adapt its colouration to its 

 surroundings, and that it can be made to change at will. 



6. In 'A History of Scandinavian Fishes,' p. 750, it is 



remarked of the Tench that in clear water " the 



whole body is yellowish green on a golden ground, with fine, 



golden dots, at the tip of each scale When it is found 



in the forest tarns, where the water is generally very dark, the 

 entire upper part of the body is black, as though dipped in ink, 

 only the belly being somewhat lighter." As the Tench in 

 aquarium 3, although dark green, and darker on the top of the 

 head and along the middle line of the back than on the under 

 parts, were certainly never so dark "as though dipped in ink," 

 I covered up the aquarium 3, with the two Tench in it, in such 

 a way that all light was excluded, and left it for a day. The 

 Tench seemed to me at the end of this time to be no darker 

 than they had been at any time in aquarium 3. Experiments 

 on these two Tench seem to show that there is a lightness of 

 yellow and a darkness of green which the fishes cannot exceed, 

 and that two hours is sufficient time to enable them to change 

 from one extreme to the other. 



7. I wished now to observe whether any effects would be 

 produced by taking a Tench from aquarium 3 and putting it 

 into a small aquarium, which had four sides of glass, and then 

 surrounding the aquarium with bright red cloth, through which, 

 for a day, a strong light passed from a window. The Tench did 

 not change from its dark green colour. 



2 d 2 



