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Show 70 DARWINISM 2 8 4 5 6 7 8 2 8 4 5 a 7 8 Fw. H.-Variation of Skull of Wolf. 10 specimens CUA P, 9 10 9 70 III VARIABILITY OF SPECIE IN A STATE OF NATURE 71 size. I noted particularly that these variations bore no necessary relation to each other, so that a large tcmpond muscle and zygomatic aperture might exist either with a large or a small cranium; and thus was explained the curious difference between the single-crested and the donhlc-crestcd skulls, which had been supposed to characterise distinct species. As an instance of the amount of variation in the skulls of fully adult male orangs, I found the width between the orbits externally to be only 4 inches in one specimen and. fully 5 inches in another. Exact measurements of large series of compamblc skulls of the mammalia arc not easily found, but from tho. c available I have prepared three diagrams (Figs. 14, 15, and. 16), in order to exhibit the facts of variation in thi. very important organ. The first shows the variation in ten specimens of the c )mmon wolf (Canis lupus) from one district in North America, and we see that it is not only large in amount, but that each part exhibits a considerable independent variability.1 In Diagram 15 we have the variations of eight skulls of the Indian Honey-bear (U rsus labiatu ), as tabulated by the late Dr. J. E. Gray of the British Museum. .For snch a, small number of specimens the amount of variation is very large-from one-eighth to one-fifth of the mean siL:c,- whilc there arc an extraordinary number of instances of independent variability. In Diagram 16 we have the length and width of twelve skulls of adult rna los of the Indian wild boar (Sus cristatus), also given by Dr. Gray, exhibiting in both sets of measurements a variation of more than one-sixth, combined with a very considerable amount of independent variability. 2 The few facts now given, as to variations of th intenml parts of animal, might be multiplied indefinitely hy a scan;h through the volnminons writings of cornpamtivc anatom i ~t~. But the evidence already adduced, taJccn in conjunction with the much fuller evidence of v:11·iation in all external org;tns, leads us to the conclusion that wherever variation arc looked for among a considerable uumbcr of individuals of the more 1 J. A. Allen, on Gcographi('a] Variation among North Americau Mammals, Bull. U. S. Geol. nnd Geog. Snrvey, vol. ii. p. 314 (1876). 2 P?·oc. Zool. Soc. Loud., 1864, p. 700, am! 1868, p. 28. |
