[ 53 ] 



Additional Evidence on the Influence of Light in 



producing Pigments on the Lower Sides 



of Flat Fishes. 



By 

 J. T. Cunningham, M.A. 



I. An Observation on Plaice and Flounders. 



In a communication to the Eoyal Society {Phil. Trans, vol. clxxxiv. 

 1894, and in this Journal, vol. ii. no. 1), I described a series of 

 experiments in which light was directed upon the lower sides of flat 

 fishes, by means of a tank with a glass bottom, and a mirror placed 

 beneath it. I have now to record an observation which confirms my 

 previous results in a most striking manner. Curiously enough, the 

 effect I am about to describe, in some respects even more important 

 as evidence than those obtained in my experiments, was observed 

 accidentally, or at least incidentally, and was due to conditions which 

 had been quite unintentionally produced. 



On December 31st, 1894, I examined all the flat fishes which had 

 been kept in a certain tank, for the purpose of ascertaining their rate 

 of growth. These fishes were five in number, namely : 



1 plaice . 8^ in. long. 1 flounder . 6| in. long 



1 » • >i » 1 « . o| ,, 



1 sole . 5| in. long. 



There were no other flat fishes in the tank, which was one of the 

 table-tanks in the Laboratory of the Association, at Tlymouth. It was 

 5 ft. long, 2 ft. G in. wide and 15 in. deep, and its sides and bottom were 

 of slate, the front of glass. I was surprised to notice that all these flat 

 fishes were partially pigmented on their lower sides. At first this 

 appeared to be a complete nullification of the conclusions drawn from 

 my previous experiments, but further examination of the matter gave it, 

 a different interpretation. 



