horses (Phyllopteryx sp.) "closely resemble the colour of seaweeds to which they attach themselves, while the filamentous appendages of their spines appear as if they were actually a part of the vegetable growth."[1] The Dragonfly larva "trusts chiefly to its sombre colouration and its motionless attitude. The larva clinging to a stem in the shady recesses of water-weeds is not easily distinguished, and the absence of movement removes the chief risk of discovery."[2] Many caterpillars resort to the bark of trees, with which their colour and often notched, knotted, or spotted bodies closely assimilate. That this is a form of active mimicry may be gleaned from the remarks of a British entomologist:—"A number of these mimics of the insect world never venture to feed by day, but take in their quantum of provision during the dark hours, and practise their deceptions during the day."[3] Active mimicry may also explain resemblances which Weismann is very emphatic in denying as due to "external influences." "If a caterpillar, which hides itself by day in the crevices of the bark, possesses the same colour as the latter, whilst other caterpillars which rest on leaves are of a green colour, these facts cannot be explained as the result of the direct influence of the bark and leaves. And it would be even less possible to explain upon the same principle all the details of marking and colour by which these animals gain still further protection. If the upper side of the upper wings of certain moths is grey like the stone on which they rest by day, while in butterflies the under side of both wings which are exposed during rest exhibits analogous protective colours, these facts cannot be due to the direct influence of the surroundings which are resembled; but, if they have arisen in any natural manner, they must have been indirectly produced by the surroundings."[4] These last remarks appear to be obscure. Surely, to make the proposition clear, some explanation should have been given as to what is meant to be differentiated between "cannot be due to the direct influence of the surroundings," and "must have been indirectly produced by the surroundings." And therefore, per-
