Ill VARIABILITY OF SPECIES IN A STATE OF NATURE 71 



size. I noted particularly that these variations bore no 

 necessary relation to each other, so that a large temporal 

 muscle and zygomatic aperture might exist either Avith a 

 large or a small cranium ; and thus Avas explained the curious 

 difference betAveen the single-crested and the double-crested 

 skulls, Avhich 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 AA'idth 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 shoAA^s the variation in ten specimens of the common 

 Avolf (Canis lupus) from one district in Korth America, and 

 Ave see that it is not only large in amount, but that each 

 jmrt exhibits a considerable independent A^ariability.-^ 



In Diagram 15 Ave 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, — Avhile 

 there are an extraordinary number of instances of inde- 

 pendent A'ariability. In Diagram 16 avc have the length and 

 Avidth of tAvelve skulls of adult males of the Indian AAald boar 

 (Sus cristatus), also given by Dr. Gray, exhibiting in both sets 

 of measurements a variation of more than one-sixth, combined 

 \Adth a very considerable amount of independent variability.^ 



The feAV facts noAV given, as to variations of the internal 

 parts of animals, might be multiplied indefinitely by a search 

 through the voluminous AAritings of comparative anatomists. 

 But the evidence already adduced, taken in conjunction Avith 

 the much fuller eAddence of variation in all external organs, 

 leads us to the conclusion that Avherever A^ariations are looked 

 for among a considerable number of individuals of the more 



^ J. A. Allen, ou Geogi'aphical Variation among Nortli American Mammal 

 Bidl. U. S. Oeol. and Geog. Survey, vol. ii. p. 314 (1876). 

 2 Proc. Zool. Soc. Lond., 1S64, p. 700, and 1868, p. 28, 



