ON COLOURS IN NATURE. 91 
pretty certain to be several exceptions to the rule as regards 
cause and effect in colour, partly, it may be, arising from 
incompleteness of knowledge and imperfection of experiment 
as yet, while only on the threshold and borderland of an almost 
untrodden fieid, and same reasons, moreover, when no results 
are attainable from a brood of caterpillars suddenly dying out 
by reason of an epidemic or otherwise. 
Again, with regard to colour in animals generally,—not in- 
sects only, but all living creatures viewed as one great whole, 
—certain great truths are sufficiently manifest. First, the 
relation between colouring and light is very evident in beings 
which inhabit the earth and air, and in some instances, but by 
no means in all, and not in the same way or to the same ex- 
tent in those of the water also. Many statements have been 
given in support of this, several of which I unhesitatingly 
admit, while others I accept subject to certain qualifications 
and reserve. It has been asserted with regard to the denizens 
of earth and air, that those are the most brilliant which are 
exposed to the sun; those of the tropics are brighter than in 
the regions around the North Pole, and the diurnal species 
than the nocturnal. But it should be borne in mind, that to 
institute a comparison between the tropics and the neighbour- 
hood of the North Pole in reference to any order in Nature, 
is to pre-suppose two extreme cases, and the fact is ignored, 
that though the tropics possess a far greater number of rich 
and radiant-coloured birds and insects than any other part of 
the globe, they contain at the same time many more dull- 
coloured ones as well,—butterflies, at all events. And while 
dwelling on the subject of diurnal Lepidoptera, with which 
tribe I am most familiar, I may take the opportunity of men- 
tioning that our seven British species of genus Vanessa equal 
in beauty any other kinds of the same family from warmer 
climates. Again, it has been stated, and stated truly, that 
birds which fly, as it were, bathed in light, do not offer the 
strong contrast of tone between the upper and lower side ; 
in other words, that the breast resembles the head, or back, 
or wings, one or other if not all of these in colouring, I 
‘ suppose. But the writer of the article that appeared several 
years ago in Chambers’s Journal, and from which I am now 
quoting, adds, “ And the wings of many butterflies are as 
beautifully feathered below as above.”  As_ beautifully 
feathered,—yes ; but very differently coloured, and very 
differently marked. I have in my mind’s eye at this moment 
three different species of the South American genus Cata- 
gramma, that may serve as one example out of many that I 
