. Darwinism : an exposition of the theory of natural selection, with some of its applications. Natural selection; Evolution. Ill VARIABILITY OF SPECIES IN A STATE OF NATURE 71 size. I noted particularly that these variations hore no necessary relation to each other, so that a large temporal 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 double-crested skulls, which had been supposed to characterise distinct species. As an instance of the amount of variation in the skulls of fully
. Darwinism : an exposition of the theory of natural selection, with some of its applications. Natural selection; Evolution. Ill VARIABILITY OF SPECIES IN A STATE OF NATURE 71 size. I noted particularly that these variations hore no necessary relation to each other, so that a large temporal 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 double-crested 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 betAveen the orbits externally to be only 4 inches in one specimen and fully 5 inches in another. Exact measurements of large series of comparable skulls of the mammalia are not easily found, but from those available I have prepared three diagrams (Figs. 14, 15, and 16), in order to exhibit the facts of variation in this very important organ. The first shows the variation in ten specimens of the common 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 ^ In Diagram 15 we have the variations of eight skulls of the Indian Honey-bear (Ursus labiatus), as tabulated by the late Dr. J. E. Gray of the British Museum. For such a small number of specimens the amount of variation is very large—from one-eighth to one-fifth of the mean size,—while there are an extraordinary number of instances of inde- pendent variability. In Diagi'am 16 we have the length and "width of twelve skulls of adult males of the Indian A^ld boar (Sus cristatus), also given by Dr. Gray, exhibiting in both sets of measurements a variation of more than one-sixth, combined mth a very considerable amount of independent The few facts now given, as to variations of the internal parts of animals, might be multiplied indefinitely by a search th
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