the Varieties of Animals. 41 



in size, or in colour; but is vague in the degree of being alike 

 used to denote the slightest individual variation, and ihe most 

 dissimilar breeds which have originated from one common 

 stock. The term is, however, quite inapplicable to an animal 

 in any state of periodical change natural to the species to 

 which it belongs. 



Varieties require some classification; and though I feel 

 myself hardly adequate to the task, I shall here propose to 

 arrange them under four principal heads ; in the hope that 

 this endeavour will induce some naturalists, more competent 

 than myself, to follow out this intricate and complicated sub- 

 ject, into all its details. 



I would distinguish, then, what are called varieties, into 

 simple variations, acquired variations, breeds, and true varieties. 

 These appear, in general, sufficiently distinct, although the 

 exact limits of each are sometimes vevy difficult, to be assigned. 

 Indeed, in many cases they only differ in degree, and in 

 others they may be all combined in one individual. Moreover, 

 the varieties of either class have a much greater tendency to 

 produce varieties of another class, than the typical animals of 

 a species have to produce any sort of variety. 



I. Simple Variations. — The first class, which I propose to 

 style simple or slight individual variations, differs only in degree 

 from the last, or true varieties ; and consists of mere differences 

 of colour or of stature, unaccompanied by any remarkable 

 structural deviation; also of slight individual peculiarities of 

 any kind, which are more or less observable in all animals, 

 whether wild or tame, and which, having a tendency to per- 

 petuate themselves by generation, may, under particular cir- 

 cumstances, become the origin of true breeds (which constitute 

 my third class of varieties), but which, in a stale of nature, 

 are generally lost in the course of two or three generations. 

 Albinoes belong to this first division, and also the other 

 numerous anomalies mentioned in VII. 589 — 591. 593 — 598. 

 These simple variations occur both in wild and in domestic 

 animals, but are much more frequent in the latter, and are 

 commonly observed in all breeds and true varieties. 



Among the Mammalia, total or partial absence of colour is 

 always, I believe, continued through life ; excepting, of course, 

 the cases of mere seasonal change; and, in this class of animals 

 generally, perfect albinoes are much more numerous than 

 among birds. Perfect albinoes are peculiar to warm-blooded 

 animals, and in them there is a total deficiency of colouring 

 matter in the rete mucosum, and, consequently, in the fur, 

 and even the pigmentum nigrum of the eye is entirely want- 

 ing. In birds, these perfect albinoes are extremely rare, 



