130 THE entomologist's RECORD. 



afterwards by Darwin, gave a clue to the cause of this resemblance, 

 and, although, as we have already said, we prefer Weismann's view 

 (the presence of " variational units " in every germ), to that of 

 Darwin, to account for the presence of the elements of variation in 

 the organism itself, yet, there can be no doubt that the theory of 

 selection, by which useful variations are seized upon and adapted to 

 specific ends, in directions useful to the individual, explains how these 

 marvellous resemblances have been brought about, and how insects 

 have become assimilated in superficial appearance to the vegetable or 

 inorganic substances on which or among which they may rest. 



The application of the Darwinian principle to this particular phase 

 of protective resemblance was worked out at length by Wallace. He 

 writes : — " The other species to which I have to direct attention is 

 the Kalliiim paralckta, a butterfly of the same family group as our 

 Purple Emperor, and of about the same size or larger. Its upper 

 surface is of a rich purple, variously tinged with ash colour, and 

 across the fore-wings there is a broad bar of deep orange, so that, when 

 on the wing, it is very conspicuous. This species was not uncommon 

 in dry Avoods and thickets, and I often endeavoured to capture it 

 without success, for, after flying a short distance, it would enter a 

 bush among dry or dead leaves, and, however carefully I crept up to 

 the spot, I could never discover it, till it would suddenly start out 

 again and then disappear in a similar place. At length, I was 

 fortunate enough to see the exact spot where the butterfly settled, 

 and, though I lost sight of it for some time, I, at length, discovered 

 that it was close before my eyes, but that, in its position of repose, it 

 so closely resembled a dead leaf attached to a twig, as almost certainly 

 to deceive the eye, even when gazing full upon it. I captured several 

 specimens on the wing, and was able fully to understand the way in 

 which this wonderful resemblance is produced. The end of the upper 

 wings terminates in a fine point, just as the leaves of many tropical 

 shrubs and trees are pointed, whilst the lower wings are somewhat 

 more obtuse, and are lengthened out into a short thick tail. Between 

 these two points there runs a dark curved line, exactly representing 

 the midrib of a leaf, and from this radiate on each side a 

 few oblique marks, which well imitate the lateral veins. These 

 marks are more clearly seen in the outer portion of the 

 base of the wings and, on the inner side, towards the middle 

 and apex, and they are produced by stria) and markings which 

 are very common in allied species, but which are here modified and 

 strengthened so as to imitate more exactly the venation of a leaf. 

 The tint of the under surface varies much, but it is always some ashy 

 brown or reddish colour, which matches with those of dead leaves. 

 The habit of the species is always to rest on a twig and among dead 

 or dry leaves, and, in this position, with the wings closely pressed 

 together, their outline is exactly that of a moderately-sized leaf, 

 slightly curved or shrivelled. The tail of the hind-wings forms a 

 perfect stalk, and touches the stick, while the insect is supported by 

 the middle pair of legs, which are not noticed among the twigs and 

 fibres that surround it. The head and antenn* are drawn back 

 between the wings, so as to be quite concealed, and there is a little 

 notch hollowed out at the very base of the wings, which allows the 

 head to be retracted sufliciently. All these varied details combine 



