each season being generally all that are taken. It is usually found on the leaves of young trees, from twelve to twenty feet from the ground. I have taken the rather heavy-bodied female by throwing a stone at it and causing it to fall within reach, but the male is more active on the wing, and it was long before I obtained a specimen.

Amongst the insects of Chontales none are more worthy of notice than the many curious species of Orthoptera that look like green and faded leaves of trees. I have already described one species that resembles a green leaf, and so much so that it even deceived the acute senses of the foraging ants; other species, belonging to a closely

related genus (Pterochroza), imitate leaves in every stage of decay, some being faded-green, blotched with yellow; others, as in the species figured, resemble a brown withered leaf, the resemblance being increased by a transparent hole through both wings that looks like a piece taken out of the leaf. In many butterflies that resemble leaves on the under side of their wings, the wings being raised and closed together when at rest so as to hide the bright colours of the upper surface, there are similar transparent spots that imitate holes; and

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MOSS INSECT.

others again are jagged at the edge, as if pieces had been taken out of them. Many chrysalides also have mirror-like spots that resemble holes; and one that I found hanging from the under side of a leaf had a real hole through it, formed by a horn that projected from the thorax and doubled back to the body, leaving a space between. Another insect, of which I only found two specimens, had a wonderful resemblance to a piece of moss, amongst which it concealed itself in the daytime, and was not to be distinguished except when accidentally shaken out. It is the larval stage of a species of Phasma.

The extraordinary perfection of these mimetic resemblances is most wonderful. I have heard this urged as a reason for believing that they could not have been produced by natural selection, because a much less degree of resemblance would have protected the mimetic species. To this it may be answered, that natural selection not only tends to pick out and preserve the forms that have protective resemblances, but to increase the perceptions of the predatory species of insects and birds, so that there is a continual progression towards a perfectly mimetic form. This progressive improvement in means of defence and of attack may be illustrated in this way. Suppose a number of not very swift hares and a number of slow-running dogs were placed on an island where there was plenty of food for the hares but none for the dogs, except the hares they could catch; the slowest of the hares would be first killed, and the swifter preserved. Then the slowest-running dogs would suffer, and having less food than the fleeter ones, would have least chance of living, and the swiftest dogs would be preserved; thus the fleetness of both dogs and hares would be gradually but surely perfected by natural selection, until the greatest speed was reached that it was possible for them to attain. I have in this supposed example confined myself to the question of speed alone, but in reality other means of pursuit and of escape would come into play and be improved. The dogs might increase in cunning, or combine together to work in couples or in packs by the same selective process; and the hares on their part might acquire means of concealment or stratagem to elude their enemies; but, on both sides, the improvement would be progressive until the highest