174 
COLOURS AND COLORATION IN ANIMALS. 
Aug., 1892. 
prevailing colours in tropical countries are yellows, reds, 
greens, and browns ; in temperate and arctic regions they 
are blacks, greys, yellows, and whites. In some cases the 
multitudinous factors which make up the environment pro¬ 
duce very marked results. Thus in Ceylon the marine as well 
as the insect fauna is prevalently green, even echinoderms 
and corals being of that colour. Probably another example 
of the action of environment is a butterfly in Argentine, 
which is exceedingly like the European Vanessa levana , and 
even has a variety like that of the latter, but belongs to a 
different genus. If the two forms occurred in the same region 
it would be said to be a case of mimicry, but as this is 
evidently not the case, is it not probable that some resem¬ 
blances between animals inhabiting the same country may 
equally be not due to mimicry ? 
Again, another example of the effect of external conditions 
on colour is probably shown by the celebrated fauna of various 
natural caves such as those of Kentucky, where darkness ever 
reigns. The animals of these caves are numerous and varied; 
they are all nearly or quite blind, and are all nearly 
white, a phenomenon due to the absence of pigment. This 
colourless condition has been supposed to be an argument for 
the purposefulness of colour where it is present, since it is 
thought to have disappeared in this case because it is useless. 
To this conclusion, however, Mr. Beddard objects ; for, says 
he, colour is allowed to be a normal product of organisation 
and not to owe its origin to natural selection ; therefore, even 
if natural selection ceases to act it ought to be present 
whether the coloration produced is useful or not, though the 
latter, indeed, may become irregular. Since, then, colour is 
absent, though it ought to be present, it looks as though 
the absence of pigment is due to environmental conditions, 
a theory supported by Mr. Poulton’s observation, that an 
amphibian, which when brought from the caves of Adelsberg, 
was colourless, became darker on continued exposure to 
light. 
In the instances just quoted it seems certain that other 
agents than natural selection have affected the colours and 
coloration; it is probable, therefore, that in various other 
cases the coloration has not been developed by natural 
selection and has not the purpose which is usually ascribed to 
it. This conclusion is supported by the following among 
other instances. 
In the case of “red snow ” and the green of most plants, 
it is clear that the coloration is not adapted to a particular 
end, and this seems true, also, in some cases where there is a 
