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When the larvte were about half grown I removed some of those 
feeding on sallow to the cylinder containing the birch, but at that 
period of life the colour had become fixed, and as far as I could 
discover there was no change whatever, and they remained a pale 
green to the last. 
Another larva, which has come before my notice this year, was a 
beautiful specimen of (Jonodoutis JJidevtata. It had been feeding on a 
tree covered with lichens, and had assumed a most distinctly variegated 
form, quite unlike the ordinary form, and assimilating exactly to the 
lichens which surrounded it, although its food was oak. This of 
course is a precisely parallel case to the P. betularia, only that it was 
found in a wild state. No one could assume that direct inheritance 
had anything to do with this decided variety, which was protective to 
the highest degree, as that form is never found on any trees other than 
those which are covered with lichens. On page 96 of Darwin’s 
Orii/in of Species, I find his definition of Natural Selection. It runs 
thus : “ But if variations useful to any organic being ever do occur, 
assuredly individuals thus characterised will have best chance of being 
preserved in the struggle for life and from the strong principle of 
inheritance these will tend to produce offspring similarly characterised. 
This principle of preservation, or the survival of the fittest, I have 
called Natural Selection.” 
My contention now is that the “ strong principle of inheritance ” 
has played no part in the variation that has occurred in these larvae, 
as all the P. betularia proceeded from the same parents, and the 
varieties were produced in direct response to environment. But I am 
told, in language to me somewhat bewildering, that the power to 
assimilate has been inherited; but when we admit that, it seems to 
me that the principle of Natural Selection is very far-fetched, and is 
not in keeping with the above definition. 
If P. betularia was the only larva that assimilated to its environment 
we might perhaps then say that the power had been inherited and had 
preserved it beyond other lepidopterous larvae, but to any one who has 
the least knowledge of larvae, they must know that remarkably few 
larvae are unprotected in one way or another. Among others that 
come to my mind is the larva of Cidaria dotata, which resembles the 
mid-rib of the currant leaf on which it feeds, frequently resting along 
the mid-rib, and assuming the colour of the stalk and rib of the leaf, 
rather than the colour of the leaf itself. Other examples of protection 
are those of P/iorodesma smarapdaria and Phorodesina bajularia, both of 
which cover themselves with fragments of their foodplant, which afford 
a perfect protection. The aim of life is the same, protection from its 
enemies. I might instance numerous other examples of larva? resembling 
their immediate surroundings, such as Gemnctaa papilionaria, which 
resembles the bud of the birch before and after winter, the larva 
hybernating on the bare tw'igs of the birch. As the spring advances 
and the buds and catkins begin to show signs of green, so the colour 
of the larva alters with each change of skin, until it finally assumes a 
beautiful green, corresponding exactly with the young leaves of spring. 
Then we have a large number of-stick like larvae, perhaps the most 
perfect being the genera Emu mi os, these larvae place their fore legs 
together to represent a small spine on the twig; but many others are 
equally perfect in the resemblance to a twig. 
