216 
COLOUR IN NATURE 
CHAP. 
amount of pigment developed increased with the 
amount of exposure, and that although pigment was 
developed more rapidly when the larvae were very 
young, yet the power of developing pigment was 
not confined to any particular age. This is interest¬ 
ing as showing that the abnormal pigmentation was 
not a purely larval phenomenon as, for example, was 
the peculiar colour change shown by Fischel’s sala¬ 
manders (see Amphibians, p. 233). The illumination 
of the lower surface during the process of metamor¬ 
phosis did not in any way interfere with the ordinary 
course of development, but throughout the whole of 
the experiments Mr. Cunningham noticed that the 
larvae all had what he calls the “ objectionable 
habit ” of clinging to the sides of the tank so as to 
avoid as far as possible the illumination of the lower 
surface. This suggests that the light had some 
powerful and unpleasant influence upon the nervous 
system. The pigmentation of the lower surface was 
apparently in no case so marked as that of the 
normal upper surface, but was always the same in 
kind, and showed the same variations of colour due 
to contraction or expansion of the chromatophores 
as the upper surface. Artificially produced pigment 
always appeared first in the middle region of the 
body on each side of the lateral line, and last in the 
head and tail regions. 
Besides these artificially produced abnormalities 
in flat-fish, many cases have been described in 
which the lower surface is more or less coloured 
under natural conditions. In some cases the colour 
is due to mere ill-defined patches of pigment, but in 
others the lower or blind surface shows in whole or 
