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acquire fresh chlorophyll from the leaves. The passage of an adven 
titious colouring matter on into a second generation is a very 
remarkable phenomenon.”—.(Poulton. The Colour of Animals, 
ftp- 79~8°-) 
In this case, the green leaf causes the concealment which 
the caterpillar enjoys at once, just as the colour of the 
chemist’s bottle would be altered by the alteration of its 
contents. But that is not all. It colours the eggs which 
the caterpillar will lay when it becomes a perfect insect. 
Nor is that all; for the young caterpillar of the next 
generation is hatched green,—it is protected from the 
hour of its emergence from the egg ere it has gained the 
protection of the leaves on which it feeds. Of course, all 
the organisms undergo this change. How can this case 
be cited as a most favourable illustration of the action of 
Natural Selection? 
But sometimes, in a most marvellous manner, the green 
caterpillar changes its tints pari passu with the changing- 
colour of the autumnal leaf. In order to understand how 
this transmutation has been brought about, we must 
remember that the leaves of different plants contain, in 
various proportions, a principle known as tannin; and 
botanists tell us that the autumnal tints of leaves are due 
to the changes which tannin undergoes on exposure to 
light and air. These tints are the most splendid in the 
case of trees and shrubs rich in tannin. In such species 
a leaf or a part of a leaf accidentally screened from light 
retains its green summer colour, whilst those around have 
turned into a rich yellow, red or brown. Now, it has been 
discovered that certain insects also contain this principle 
of tannin. In the year 1810, M. Penaut, a pharmaceutical 
chemist of Bourges, found in the body of corn-weevils 
gallic acid, a compound kindred to tannin. M. Villon, 
who has been engaged for a long time in searching for