LECTURES. 39 
afraid that this is not true of clockwork, but it is certainly true of 
Nature. The fish that live in the great caves of Kentucky lose their 
sight just as surely as the man who takes no exercise loses the proper 
use of his limbs. 
In the first place then the mimic is defenceless. Next he must 
be much less common than the creature he mimics. If there were 
many more clear-wings than wasps or hornets, birds would begin to 
think it worth while attacking insects with yellow bands round their 
bodies. Lastly, the imitation, however minute, extends only to out- 
ward form and colour, and does not affect the internal character of 
the creature. 
We have mentioned a few cases of mimicry among British insects, 
but it is among Tropical forms that we find the most numerous and 
perfect specimens. As I have said, we may divide insects into. two 
classes :— 
(1). Those that sting or are inedible by reason of possessing a 
disagreeable taste. It is to the advantage of these sort of insects 
that they should be avoided, and they are generally painted in bright 
warning colours—blue and red and yellow. 
(2). Those which are edible and defenceless. Among these 
latter we find mimicry of two kind: that of inamimate objects around, 
that of their more fortunate neighbours. 
It is to Mr. Wallace, who spent many years in studying the 
Natural History of the Malay Archipelego, and Mr. Bates, who 
travelled on the Amazons, that we are largely indebted for our 
knowledge of the subject. 
Mr. Wallace was travelling with his natives one day, when they © 
came to tell him that there was a new insect among the firewood. — 
He looked at the place they pointed out, but could only see some 
bits of brown moss, when suddenly to his astonishment one of the — 
bits of moss walked off—it was a live insect. Its back was all ragged 
and was even covered with little red spots to represent tiny lichens. 
Again, a bright moth of a rich purple hue with a bright band across 
its wings attracted his attention, but whenever he pursued it, it 
suddenly vanished. At last he saw the very spot where one alighted — 
on a bush among some dead leaves, but no! it was gone. A careful 
examination shewed that it had turned into a veritable leaf attached 
by a twig to a branch, in such a way as to deceive him when gazing) 
straight at it. 4 
As Professor Drummond was travelling through Africa between” 
Lakes Nyassa and Tanganyika his native servant suddenly exclaimed 
