330 Mr Stark on Changes in the Colour (^Fishes. 



the colours and markings, for which I am unable satisfactorily 



to account. 



On the 25th July, three minnows were put into a crystal de- 

 canter, rolled all round with black silk, and placed in a dark 

 corner of the room. At this time they were brownish or sand 

 coloured on the back, sides with golden, bluish and black va- 

 riegations, belly and lower part of the sides silvery white. They 

 remained in this situation till the 3d of August, during which 

 time no change of colour took place. 



I repeated the same experiments often, and varied in all ways 

 I could think of, with the Stickleback. Its changes of colour 

 were still more remarkable than those of the minnow, inasmuch 

 as they took place much more rapidly ; and even in a few mi- 

 nutes, and under the eye, the colours may be seen to fade or 

 brighten according to the nature of the vessel they are placed 

 in for the time. The fine vermilion colour of the breast almost 

 disappears when placed in a white basin ; and the vivid colours 

 are as speedily recovered' upon transferring the animals to a 

 black glazed earthen jar. 



As the same changes in colour take place in the Loche (Co- 

 bitis barbatula), and in the Perch (Perca JluviatiUs), it is un- 

 necessary to detail experiments which are in every one's power 

 to make. The sudden change in colour which takes place in 

 the course of a few hours, is so striking, that doubts of the 

 identity of the animals might reasonably be entertained by one 

 who witnessed the results, without being aware of the circum- 

 stances which led to them. Though I retained them at first 

 for weeks in the various vessels, to ascertain the reality and 

 permanency of the change, while circumstances remained the 

 same, yet I afterwards experienced that a few hours was suffi- 

 cient to display all the phenomena. 



Into the causes of these changes of colour in fishes, and to 

 what extent these may be explained on optical, chemical or phy- 

 siological principles, I do not hazard an opinion. One prin- 

 ciple is sufficiently obvious from these experiments, that these 

 fishes, and perhaps all the other river and lake fish, possess the 

 faculty of accommodating their colour to the ground or bottom 

 of the waters in which they are found. The final reason for this 



