Note 99 — Part II. ON THE FINAL CAUSES OF TRANSFORMATION.

[In 1879 Mr. E. Boscher found about thirty full-grown caterpillars of this species in the neighbourhood of Twickenham, ten to twelve of which were feeding on Salix viminalis, and the remainder, from a locality not far distant, on Salix triandra. The whole of the specimens taken on the plant first named, had the red-brown spots above and below the oblique stripes more or less completely developed, as I myself had an opportunity of observing. In these spotted specimens the ground-colour was bright yellowish-green, and in the others this colour was dull whitish-green above, passing into bluish-green below. Should these observations receive wider confirmation, it would be fair to conclude that this species is now in two states of phyletic development, the more advanced stage being represented by the brighter spotted variety. (See also Proc. Ent. Soc. 1879, p. xliv.). Mr. Peter Cameron has recently suggested (Trans. Ent. Soc. 1880, p. 69) that the reddish-brown spots on the Smerinthus caterpillars may serve for purposes of disguise, as they closely resemble, both in colour and form, certain galls (Phytoptus) of the food-plants of these species. If this view be admitted, these spots must be considered as a new character, now being developed by natural selection. The variation in the ground-colour of the two forms of S. Ocellatus may possibly be phytophagic, but this can only be decisively settled by a series of carefully conducted experiments. R.M.]