Permanence and Evolution. 77 



and subsequent intermixture, which is a known 

 cause, and in nature, as well as under domesti- 

 cation witness the intermixture of the common 

 and Royston crows, the Tetrao urogalhts and 

 Tetrao tetrix, coupled with reversion, which is 

 also a known cause, as with that of transmuta- 

 tion, which is a cause purely conjectural. 



Let us suppose two varieties or strains of 

 horse, say white Arabs and black 'Suffolks, living 

 on adjoining areas ; we should probably see a rim 

 of animals with intermediate characters along 

 the frontier, while if the two breeds arriving 

 from opposite quarters peopled a district to- 

 gether, we should no doubt see a promiscuous 

 mass of mongrels, while if one sort were vastly 

 preponderant over the other, either in numbers 

 or prepotence, we should see a tolerably uniform 

 mass of say white Arabs, with only an occasional 

 black specimen, or one in some other way re- 

 calling the Suffolk race. I think there can be 

 no doubt that this is what any breeder would 



