1850.] Remarks on the variation of affined species. 227 



species, as the gradations continue unbroken to the most marked 

 specific types, and which still may hold a parallel in the respective 

 regions, as the peculiar Jungle-fowl and Spur-fowl (Galloperdix) of 

 Ceylon, as compared with their Indian congeners, may suffice to testify. 



In poleward or very elevated regions we remark the contrary tendency 

 of animals, to become paler in colour, whether particular species or evi- 

 dent varieties of those which inhabit elsewhere. For example, the Tibe- 

 tan fauna generally would seem to exemplify this law ; and several of 

 the birds of Scandinavia as compared with those of Britain are deficient 

 in colour, greys passing into white, and fulvous into white or grey. 

 The only difference between Sitta europcea, L. (vel S. asiatica and 

 sericea, Temminck, and S. uralensis, Lichtenstein,) of Scandinavia 

 and the northernmost parts of Europe generally, from S. ccesia of the 

 rest of Europe, consists in the lower parts of the former being pure 

 white where those of the latter are pale fulvous ; and in S. cinnamo- 

 ventris of the Himalaya, again, the only difference consists in the 

 same parts being altogether of the deep and dark ferruginous which is 

 confined to the flanks and lower tail-coverts only of the two preceding 

 races. Picus minor and Parus ater and P. palustris of Scandinavia 

 are thus readily distinguished from the corresponding races of Britain : 

 and it is curious that Orites caudatus of the N. of Europe would 

 appear to have invariably a pure white head, devoid of the dark 

 sincipital bands which occur constantly upon this species in Britain. 



There is yet another phsenomenon which adds to the difficulty of 

 discriminating species in some, though not many, instances ; and this is 

 the production of hybrid races and individuals of mixed origin of 

 every grade of intermediateness. In some cases the hybrids are not 

 known to reproduce, and so to form a race, as instanced by the mule 

 grouse of Northern Europe (the cross between the Capercailzie and 

 the Black Grouse), together with other hybrids produced by sundry wild 

 Gallinacece and Anatidce : but there are some hybrids which are quite 

 as prolific as their parents, as among mammalia those raised between, 

 the humped and humpless domestic cattle, and among domestic birds 

 the mixed progeny of Anser cinereus and A. cygnoides.* So in the 



* All the domestic Geese of India (so far as I have seen) are of this mixed 

 species, and in no animals can specifical characters be more strongly marked than 

 in the parent races, extending to the voice and habits. So with the cattle, — the 



