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Show 136 DAH.WINISM ' I!A P. Bronn relates to this very point. He states that the length of these organs differ in the v~.rio~s species of hares and of mi?c, and he considers that th1s difference can be of no scrv1cc whatever to their possessors. But to this objection Darwin replies, that it has been shown by J?r. Schobl that ~he cars of mice "are supplied in an cxtraordmary ma.nner with nerves, so that they no doubt sc~·ve a~ tactile organs." Hcn?o, whc_n we consider the life of miCe, either nocturnal or seekmg th01r food in dark and confined places, the length of the ears mn.y be in each case adapted to ~he partic~l~r habits n.n<l surroundino-s of the species. Agam, tho t~ul, 111 tho larger mammals ~ftcn serves the purpose of driving off flies and other ins~cts from the body; and when we con ·idor in how mn.ny parts of the world flies are injurious or oven fatal to large mammals, we sec that the peculiar chara_ctoristic.s of this oro-an may in each case have been adapted to Its rcqmrcmcnts in °thc particular area where the species was developed. The tail is also believed to have some usc as a balancing org:1n, which assists an animal to turn easily and rapidly, much a~ our arms are used when running; while in whole groups it is a prehensile organ, and has become modified in accordance with the habits and needs of each species. In the case of mice it is thus used by the young. Darwin informs us Uw t the late Professor Henslow kept some harvest- mice in confinement, and observed that they frequently curled their tails round the branches of a bush placed in the en o·c, and thns aided themselves in climbing; while Dr. Gunther has actually seen a mouse suspend itself by the tail (Origin, p. 18 9 ). Again, Mr. Lawson Tait has called attention to the usc of the tail in the cat, squirrel, yak, and many other animals ns a means of preserving the heat of the body during the nocturnal and the winter sleep. He says, that in cold weather animals with long or bushy tails will be found lying curled up, with their tails carefully laid over their feet like a rug, and with their noses buried in the fur of the tail, which is th ns used exactly in the same way and for the same purpose as we usc respirators.1 Another illustration is furnished by the horns of deer which, especially when very large, have been supposed to he 1 Natu1·e, vol. xx. p. 603. VI DIFFICULTrES AND OfUECTlONS 137 a .danger to the. animal in passing mpidly through dense thickets. B~t S1r James H~ctor states, that the wapiti, in North Amenca, throws back Its head, thus placincr the horns along the sides of the back, and is then enabled to ru. h through the thickest forest with great rapidity. The browantlers protect. t~e face and eyes, while the widely spreading hor.ns prevent ll~Jury to the neck or flanks. Thus an orga.n wh1eh was ccrtamly developed as a sexual weapon, bas been so guided and modified during its increase in size as to be of usc in other ways. A similar use of the antlers of deer has been observed in India.l The various classes of facts now referred to serve to show us that, in the case of the two higher groups-mammali<t and birds-almost all the characters by which species arc distinguished from each other arc, or may he, adaptive. It is these two classes of animals which have been most st~diccl and whose life-histories are supposed to be most fully known, yet even here the assertion of inutility, by an eminent naturalist, in the case of two important organs, has been sufficiently met by minute details either in the anatomy or in the habits of the groups referred to. Such a fact as this, together with the extensive series of characters alrca.dy enumerated which have been of bte years transferred from the "useless" to the "useful " class, should convince us, that the assertion of "inutility" in the case of any organ or peculiarity which is not a rudiment or a correlation, is not, and can never be, the statement of a bet, but merely an expression of our ignorance of its purpose or origin. 2 1 Nattt?·e, vol. xxxviii. p. 328. 2 A very remarkable illustration of function in an apparently useless ornament is given by Semper. lie say:, "It is known that the skin of reptiles encloses the body with scale. . These scales are distinguishe<l l1y very various sculpturings, highly characteristic of the different spec ieH. Irrespective of their systen1atic siguitlc:mce they appear to be of no value in the life of the animal ; indeed, they are viewed a-; ornamental without reganl to the fact that they are microscopic azHl much too delicate to be visible to other animals of their own species. lt might, therefore, :eem hopeless to show the necessity for their existence 011 Darwinian principles, azHl to prove that th~y ar_e physiologically active organs. Neverth eless, recent investigations on thzs pomt have furnisher! eviden ce that this is possible. "It is known that many reptil es, and above all the snakes, cast off the wh?le ·kin at once, whereas human beings do so hy degrees. H l1y any acczdent they are prevented <loiug so, they infallibly Lli e, b •cause the old |