23 
through their skins or the silk of the cocoon has been tinted. No, 
it is more rational to account for the phenomenon by natural 
selection, and to come to the conclusion that those insects which 
resemble the colour of the soil upon which they settle will be more 
fully protected from discovery than those less fortunate relatives, 
which are unable to conceal themselves, and that heredity will 
-eomplete the work. Something of this sort evidently occurs in the 
neighbourhood of coal mines and smoky manufacturing cities, 
where negro varieties are mostly to be found. 
Food has pretty generally been looked upon as an important 
factor in producing variation, but in the present day its influence 
is considered very feeble; still, there is evidence to show that it 
“possesses a certain amount of power. We have accounts of a diet 
-of madder causing some species to be turned brown. Certain 
grasses are said to darken the colour of the drinker moth, pale 
tiger moths.are stated to be bred from lettuce, dark ones from 
coltsfoot, yellow Brussel’s lace moths from yellow lichens, besides 
many others which require the confirmation of repeated experi- 
ments; but there can be no doubt that feeding is productive of 
considerable modification in the perfect insect. Feeding over an 
-extended period, particularly if followed by a long duration of the 
-chrysalis state, yields the finest moths and butterflies, those 
which are fed up quickly under the stimulus of warmth and fresh 
juicy food are comparatively small. Starvation will change the 
tone of the colour to a sickly yellowish hue; it will also render 
‘dull the bright tints, and of course dwarf the specimens. Irregular, 
-eareless feeding, sometimes with an abundance of fresh food, at 
-others with nothing at all, cr at the most with dry stale food, has 
been known to produce varieties of such species as can survive the 
treatment. 
Light, or the deficiency of it, was at one time expected to exert 
-an influence, but no satisfactory results have been recorded. With 
-decomposed light, my old friend, the late Edward Hopley, some 
thirty years ago, made a series-of experiments by covering his jam 
pot cages with different coloured glasses, but the outcome was of a 
negative nature. I did a little myself in that way, with similar 
provoking results; but I found that I could induce noctural 
caterpillars to feed in the daytime by covering the cage with blue 
or green glass, and thus make them feed up more rapidly. The 
wonderful effect of altering the colour of the chrysalis to pale, dark 
or gold, or its cocoon to the tint of the surface upon which it spins 
up by compelling the caterpillar to change in a box lined with 
coloured or gilded paper, described by Professor Poulton in his 
charming book on Colour, is most interesting, but it is not followed 
‘by any appreciable variation in the perfect insect. 
