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 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 ^Wdth between 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 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. ^ 



In DiagTam 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 Diagram 16 we have the length and 

 Avidth of twelve skulls of adult males of the Indian aWM 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.- 



The few facts now given, as to variations of the internal 

 parts of animals, might be multiplied indefinitely by a search 

 through the voluminous ^vritings of comparative anatomists. 

 But the evidence already adduced, taken in conjunction with 

 the much fuller evidence of variation in all external organs, 

 leads us to the conclusion that wherever variations are looked 

 for among a considerable number of individuals of the more 



^ J. A. Allen, on Geogi-aphical Variation amonf:^ North American Mammals, 

 Bull. U. S. Geol. and Geog. Survey, vol. ii. p. 314 (1876). 

 2 Proc. Zool. Soc. Lond., 1864, p. 700, and 1868, p. 28. 



