VARYING COLOURS IN FISHES. 79 



can be effected upon the hues of fishes m a way 

 which must be widely different from the foregoing, 

 has repeatedly been demonstrated by actual experi- 

 ments. Thus, to refer to the last which have been 

 published, Mr. Shaw, Drumlanrig, procured two 

 large earthen-ware vessels, the one nearly white 

 inside, and the other nearly black. He then placed 

 a healthy Parr in each, while a constant supply of 

 fresh water was maintained. The fishes when put 

 into the vessels were of their natural colour; but 

 they had not remained in their new position more 

 than four minutes when each gradually assumed a 

 colour nearly approaching to that of the respective 

 vessel into which it had been introduced. He then 

 frequently exchanged the position of the two fishes, 

 and the result uniformly followed ; the fishes chang- 

 ing their colour according to the surface around 

 them. He next placed both fishes in one basin, 

 when the contrast for a short time was exceedingly 

 striking. With the view of ascertaining what effect 

 the hght had in producing the extraordinary change, 

 the fish w^ere allowed to remain in the white basin 

 till they effectually attained the pale tint ; the light 

 w^as then excluded by covering it with a thick mat ; 

 on removing which, a few minutes afterwards, the 

 fish were again changed to a dark colour; which 

 disappeared gradually on exposure to light : the 

 change being produced alike under a bright and 

 cloudy sky. Though at the time Mr. Shaw was 

 unacquainted with the fact, it must have been gene- 

 rally known that Dr. Stark of Edinburgh had several 



