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Show 202 DARWINISM OHAP. to Sm·inarn (181 0), had already explained the ~atter. He says : "The colour and even the ~hapo of t?c ha~r are much like withered moss, and serve to hide the annnal m the trees, but particularly when it has that orangc-c~lourcd spot between the shoulders and lies close to the tree; It looks then exactly like a piece of branch where the rest has been broken off: by which the hunters are often deceived." Even such a huge animal as the giraffe is said to be perfectly concealed by it" colour and form when standing among the dead and broken trees that so often occur on the outskirts of the thickets where it feeds. The largo blotch-like spots on the skin and the strano·e shape of the head and horns, like broken branches, so tend to its concealment that even the keen-eyed natives have been known to mistake trees for giraffes or giraffes for tr ' R. Innumerable examples of this kind of protective colouring occur amona insects; beetles mottled like the bark of tr es or rcsemblina the sand or rock or moss on which they live, ·with green cat:rpillars' of the exact general tints of the foliage th{'y feed on; but there arc also many C<t. ·cs of detailed imit;ttion of particular objects by insects that must be brieRy described. I Protective Irnitation of Pa1"limln1· ObJects. The insects which present this kind of imitation most perfectly are the Phasmidre, or stick and le~tf insects. The well-l 'Vith reference to thi. general resemblan ce ofinsects to th eir Pnvironment the followin()' remarks by Mr. Poulton are very instru ctive. lJe RayR : "Holding th~ larva of Sphinx lignstri in one l1and and a twi g of its foodplant in the other, the wonder we feel is, not at the J'e ·emblance huL at the difference· we are surpri. ed at the diffi culty experienced in <lctecting so I'Oll· spicuous ~n object. Ancl yet tl1e protection is very real, for the l arva~ will l>e passed over by those who are not accustom ed to th eir n~pear:w ce , al thou?h the searcl1er may be tol<l of the presence of a large caterpillar. Au expcnenee<i entomologist may also fail to find the larvm till after a considcmhle s\'arel l. '!'his is general protective rese111hlance, and it depencls upon a getwral han110n.y between the appearanc of the organi. m and its whole environment. . ft ts in1possible to und e r~>tnn<l the fm·ce of this protecLion for any lar va, wtll.IOI~t seeing it on its food -plant :t~Hl in an entirely normal condition. 'J'I1e ml1~l1 · effect of green foliage i~ more complex than we often imagine; num: lt•rl<'ss modifications are wrought by varied lights m1d shadows npon colours wlmh nrc iu themselve far from uniform. ln the larva of Papilio machaou the protection is very real wll l' ll the larva is on the food -plant, an<l can l1anlly be appreciate<! at nil when the two are apart." Numerous oth er examples arc given in the clmpter 011 "Mimicry and otl1er Protective H.esemblances among Animal:," iu IllY Cvntr·ibutions to the T!teory of Natttral Selection. VIII ORIGIN AND USES Ol! COLOUR IN ANIMALS 203 known leaf-insects of Ceylon and of Java, species of Phyllium, arc so wonderfully coloured and veined, with leafy expansions on the legs and thorax, that not one person in ten can see them when resting on the food-plant close beneath their eyes. Others resemble pieces of stick with all the minutire of knots and branches, formed by the insects' legs, which arc stuck out rigidly and nnsymmetrically. I have often been ·unable to distingui. h between one of these insects and a real piece of stick, till I satisfied myself by touching it and found it to l>C alive. One species, which was brought me in Borneo, was covered with delicate semitransparent green foliations, exactly resembling the hepaticro which cover pieces of rotten stick in the damp forests. Others resemble dead leaves in all their varieties of colour and form; and to ·how how perfect is the protection obtained and how important it is to the po sessors of it, the following incident, observed by Mr. Belt in Nicaragua, is most instructive. Dcseribing the armies of foraginO' ants in the forest which devour every insect they can catch, he says: "I was much surprised with the bch<wiour of a grcon leaflike locust. This insect stood immovably among a host of ants, many of which ran over its legs without ever discovering there was food within their reach. So fixed was its instinctive knowledge that its safety depended on its immovability, that it allowed me to pick it up and replace it among the ants without making a single effort to escape. This species closely resembles a green leaf." 1 Caterpillars also exhibit a considerable amount of detailed resemblance to the plants on which they live. Grass-feeders are striped longitudinally, while those on ordinary leaves are always striped obliquely. Some very beautiful protective resemblances are shown among the caterpillars figured in Smith and Abbott's Lepidoptermts Insects of Geurgitt, a work published in the early part of the century, before any theories of protection were started. The plates in this work aro most beautifully executed from drawings made by Mr. Abbott, representing the insects, in every case, on the plants which they frequented, and no reference is made in the clc'icriptions to the remarkable protective details which appe<tr upon tho plates. We have, first, the larva of Sphinx fuciformis feeding 1 '/'he Nat·urulist ·in Nicaraguu, p. 19. |