IN FISH. 95 



in which the fish had been living. Our experiments seem to prove 

 that coloured light has no effect except in so far as it approximates 

 to black or white. Bright light alone is not sufficient to affect the 

 pigment cells to any appreciable extent. A fish placed in a globe 

 of clear glass and exposed to the fullest sunlight retains its normal 

 colour. Nor does absolute darkness effect any marked change. 

 A series of trials carried on with great care have shown that a fish 

 whose shade of colour has been artificially heightened will, on 

 being taken into the dark, and there placed in a vessel of the 

 contrary colour to that in which it had recently been, lose the 

 abnormal colouring and resume the original shade, but will not be 

 affected farther by the colour of the vessel to which it has been 

 changed. There can be no doubt that the eye is the medium by 

 which the effects of reflected light is conveyed to the brain. Fish 

 naturally blind, as well as those which have been made blind, are 

 always normal in shade, and cannot be influenced by changes of 

 the ground colours. It would thus appear that all changes to 

 lighter or darker, are due to a certain amount of excitement caused 

 by the reflected light of the ground over which they are floating. 

 M. Georges Pouchet, who has made some observations on Sea- 

 Fish at the Aquarium of Concarneau, has come to the same con- 

 clusion ; and, in endeavouring to follow out the means by which 

 the power of change was transmitted to the surface of the skin 

 after the nerves leave the brain, believes he is warranted in saying 

 that it is the nerve bundles, not the nerves which accompany the 

 vessels, which are the real regulators of the function. Our fish 

 have been so small that we have been unable to follow the experi- 

 ments described in M. Pouchet's paper. 



The colouring matter which gives the gold tinge to most of 

 the black fish, and which appears unshaded by black in the ordi- 

 nary Gold fish, is not so well defined into separate cells as is the 

 black matter ; it is, however, subject to the same changes when 

 exposed to different kinds of light; and fish, which are only 

 yellow w^hen in a white vessel, become dark gold when placed in 

 a black vessel. In one instance, by exposing a silver fish having 

 occasional red scales on different parts of its body, to a bright 

 white reflected light, we have succeeded in causing some of the 

 red spots to disappear entirely. The converse experiment, to 



