80 CAUSES WHICH CHECK Chai\ XVI. 



continue pure." In different parts of the Falkland Islands 

 the cattle are breaking up into herds of different colours ; 

 and those on the higher ground, which are generally white, 

 usually breed, as I arn informed by Sir J. Sulivan, three 

 months earlier than those on the lowland ; and this would 

 manifestly tend to keep the herds from blending. 



Certain domestic races seem to prefer breeding with their 

 own kind ; and this is a fact of some importance, for it is a step 

 towards that instinctive feeling which helps to keep closely 

 allied species in a state of nature distinct. We have now 

 abundant evidence that, if it were not for this feeling, many 

 more hybrids would be naturally produced than in this case. 

 We have seen in the first chapter that the alco dog of Mexico 

 dislikes dogs of other breeds ; and the hairless dog of 

 Paraguay mixes less readily with the European races, than 

 the latter do with each other. In Germany the female Spitz- 

 dog is said to receive the fox more readily than will other 

 dogs; a female Australian Dingo in England attracted the 

 wild male foxes. But these differences in the sexual instinct 

 and attractive power of the various breeds may be wholly 

 due to their descent from distinct species. In Paraguay the 

 horses have much freedom, and an excellent observer * believes 

 that the native horses of the same colour and size prefer 

 associating with each other, and that the horses which have 

 been imported from Entre Eios and Banda Oriental into 

 Paraguay likewise prefer associating together. In Circassia 

 six sub-races of the horse have received distinct names; and 

 a native proprietor of rank 5 asserts that horses of three of 

 these races, whilst living a free life, almost always refuse to 

 mingle and cross, and will even attack one another. 



It has been observed, in a district stocked with heavy 

 Lincolnshire and light Norfolk sheep, that both kinds, though 

 bred together, when turned out, " in a short time separate to 

 a sheep ; " the Lincolnshires drawing off to the rich soil, and 

 the Norfolks to their own dry light soil ; and as long as there 

 is plenty of grass, " the two breeds keep themselves as 



4 Rengger, ' S'augethiere von Para- and De Quatrefages, in • Bull. Soc. 

 gaar,' s. 336. d'Acclimat.,' torn, viii., July, 1SG1, 



6 See a memoir by MM. Lherbette p. 312. 



