78 MUTUAL RELATIONS OF THE III MAN FAMILY. 



that, although they are distinguished by very marked peculiarities, yet that 

 these peculiarities are by no means consiant. There is historical evidence of 

 the great change, which may take place in their conformation and habits, 

 under the influence of a change in their external circumstances ; in the case, 

 for example, of the blood-hounds, introduced into the West Indies by the 

 Spaniards, which have now degenerated into a wild race of very different 

 form, and have lost all the distinctive characters of the breed. And there is 

 not that close agreement in the distinctive characters of the several breeds, 

 among the individuals respectively composing them, which is requisite for the 

 establishment of a definite specific distinction ; the characters being shaded 

 off, as it were in individuals, so as to cause a near approximation between the 

 less decided forms of the different races. On the other hand, in spite of the 

 varieties of conformation exhibited by the several races of Dog, (which even 

 affect the number of vertebrae in the tail, as well as the shape and proportions 

 of the bones, we never see any which present so strong a resemblance to the 

 Fox, as to be at all in danger of being mistaken for that animal ; and they 

 may always be distinguished by this obvious character, that the pupil of the 

 eye of the Dog is always round, whilst that of the Fox is oval when con- 

 tracted. This difference may appear a very trifling one, in comparison with 

 the important variations presented in the structure of the different breeds of 

 Dogs ; but it is constant ; and it may therefore be assumed to have existed 

 in the progenitors of each race, as it exists at present in all their descendants. 



66. There are many instances of an opposite character, in which the tend- 

 ency to variation is extremely small; and in which the Naturalist feels jus- 

 tified in assuming a specific difference, from variations in size or colour, 

 which in themselves are very trifling, but which are important in classifica- 

 tion, because they are constant. Thus, among the several species of the 

 genus Felis (or Cat tribe), there is scarcely any perceptible osteological varia- 

 tion, except in point of size ; so that even Cuvier was unable to find out a 

 positive means of distinguishing the skull of the Lion from that of the Tiger; 

 and the skeleton of a Wild Cat is a reduced copy of that of the largest Felines. 

 There are certain species, which are distinguished by no other external indi- 

 cations, than the markings upon their skins ; characters, which are in other 

 cases subject to extreme uncertainty ; but which are here so constant, as to 

 present scarcely the slightest variation amongst the individuals of each race. 

 Thus, if a certain patch or stripe be repeated from generation to generation, in 

 a wild feline race, the Naturalist is inclined to regard this as a sufficient proof 

 of the specific difference of that race from another which is differently marked. 

 The Domestic Cat is the only one of the group, which is liable to any con- 

 siderable variation ; and in this species, as every one knows, the markings 

 characteristic of the several breeds or races are not thus constantly repeated, 

 and therefore cannot be indicative of original difference. Now it is precisely 

 in this species ,that we should look for such variations ; since it is the only 

 one which can be domesticated; and the capability of domestication implies 

 a power in the original constitution of the animal, to adapt itself to a change 

 of circumstances, and thus to exhibit various departures from its original type. 



67. This striking contrast, between variable and invariable groups of ani- 

 mals nearly allied to each other, is found through the whole kingdom ; every 

 division of it appearing to contain some species, which do not change their 

 forms or other characteristics under any circumstances, but which cease to 

 exist if a change takes place in their conditions, incompatible with the regular 

 performance of their functions; whilst it also includes others, in whose phy- 

 sical and psychical constitutions there is such a susceptibility of modification, 

 that new forms and new instincts may arise, adapted to a great variety of 

 external conditions, and thus new and very different races may be originated. 



