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Show 204 DARWINISM CHAP. on a plant with linc:tr grass-like leaves and small blue flow.crs; and we find the insect of tho same green as the leaves, stnpcd lonaitudinally in accordance with the linear leaves, and with tho \cad blue corresponding both in size and colour with the flowers. Another species (Sphinx tcrsa) is represented feeding on a plant with small red flowers situated in tho axils of tho leaves; and tho larva bas a row of seven red spots, unequal in size, and corresponding very closely with the colour and size of the flowers. Two other figures of sphinx larv::c [tre very curious. That of Sphinx pampina.trix feeds on a wihl vine (Vi tis i ncli visa), having green tendrils, and in this species the curved horn on the tail is green, and closely imitates in its curve the tip of the tendril. But in another species (Sphinx cranta), which feeds on the fox-gmpc (Vitis vulpina), the horn is very long and reel, corresponding with the lm1g red tipped tendrils of the pbnt. Both these larvm are green with oblique stripes, to harmonise with the veined leaves of tlw vines; but a figure is al.·o given of the la. t-namcd species after it has done feeding, when it is of a decided brown colonr nnrl Juts entirely lost its horn. This is because it then descends to the ground to bury itself, ::tnd the green colour and l'('(l horn would be con picuous and dangerous; it therefore loses both at the last moult. Such a change of colom occurs in many species of caterpillars. Sometimes the change is sea.. mml; and, in those which hibernate with us, the colour of some species, which is brownish in autumn in acbptation to the fading foliage, becomes green in spring to harmonise with the newly-opened leaves at that sea. on.1 Some of the most curious examples of minute imi ta-tion a.re afforded by the caterpillars of the geometer moths, whi('h are always hrown or reddish, and rescmhlc in form little twigs of the pbnt on which they feed. They h:tvc the hal)it,, when at rest, of :tanding out obliquely from the bmn('ll, to which they hold on by their hind pair of prolcgs or claspers, and remain motionlc. s for hours. Spea,king of these protective resemblances Mr. J enncr W oir ay. : "After l>cing thirty years an entomologist I was decci vcd myself, :uul took out my pruning scissors to cut from a plum tree a spur which I thought I had overlooked. This turnccl out to be the l:trva 1 H .. Mcl<lola, in P1·oc. Zool. Soc., 1873, p. Hi5. vnr ORIGIN AND USES OF COLOUR IN ANIMAL. 205 of a gcomct r two inchc: long. I showed it to scvcml mom hers of my frunily, and. defined a sptwc of four inches in which it was to he con, but none of them could perceive that it was a caterpillar." 1 One more example of a. protected caterpillar must be given. Mr. A. Everett, writing from arawak, Borneo, says : "I had a caterpillar brought me, which, being mixed by my boy with some other thi11g., I took to be a bit of mo:s with two exquisite pinky-white seed-capsules; but I soon saw that it moved, and examining it more closely found out its real character : it is covered with hair, with two little pink spots on t.he uppm:: surface, the general hnc being more green. Its mot10ns arc very slow, and when eating the head is withdrawn beneath a fleshy mobile hood, so that the action of feeding docs not produce any movement externally. It was found in the limestone hills at Bu an, the situation of all others where mosses are mo. t plentiful and delicate, and where they partially clothe most of the protruding masses of rock." Ilow the. e Irnitations hnve been P1·od1tced. To many persons it will seem impossible that snch beautiful and detailed resemblances as those now described - and these are only samples of thousands that occnr in all parts of the wo.rld-can have been brought about by the preservation of accidental useful variations. But this will not seem so surprising if we keep in mind the facts set forth in our earlier .chapters-the rapid multiplication, the severe struggle for existence, and the constant variability of these and all other organisms. And, further, we must rcmcm ber tha~ these delicate adjustments are the result of a proce. s whiCh has been going on for millions of years, and that we now ~cc the small percentage of successes among the myriads of fmlures. From the very first appearance of insects aml their various kinds of enemies the need of protection aro c, and was usually most easily met by modification of colonr. Hen~e, we may be sure that the earliest leaf -eating insects acqmred a green colour as one of the necessities of tJ1eir existence; and, as the species became modified and specialised, 1 Natu1·e, vol. iii. p. 166. |