8 ^ ON CROSSING AS A CAUSE Chap. X\ 



same thing as their separation. In savage and 



m a 



countries, where the inhabitants have not the means of sepa 

 rating their animals, more than a single breed of the saui( 

 species rarely or never exists. In former times, even 



country so civilised as North America, there were no di; 



races of sheep, for all had been mingled together. 1 The cele- 

 brated agriculturist Marshall 2 remarks that "sheep that are 

 " kept within fences, as well as shepherded flocks in open 

 " countries, have generally a similarity, if not a uniformity, 

 ' < of character in the individuals of each flock ; " for they breed 

 freely together, and are prevented from crossing with other 

 kinds; whereas in the unenclosed parts of England the un- 

 shepherded sheep, even of the same flock, are far from true or 

 uniform, owing to various breeds having mingled and crossed 



many g 



We have seen that the half-wild cattle in the several Bril 

 parks are uniform in character in each; but in the differ 

 parks, from not having mingled and crossed during 

 rations, they differ in a slight degree. 



We cannot doubt that the extraordinary number of varieties 

 and sub-varieties of the pigeon, amounting to at least one hun- 

 dred and fifty, is partly due to their remaining, differently from 

 otlier domesticated birds, paired for life when once matched. 

 On the other hand, breeds of cats imported into this country 

 soon disappear, for their nocturnal and rambling habits render 



hardly possible to prevent free crossing. Bender 3 



&• -*- v ~"&o 



gives 



g case with respect to the cat in Paraguay 



distant parts of the kingdom it has assumed, apparently from 

 the effects of the climate, a peculiar character, but near the 

 capital this change has been prevented, owing, as he asserts, 

 to the native animal frequently crossing with cats imported 

 from Europe. In all cases like the foregoing, the effects of an 

 occasional cross will be augmented bv the increased vigour and 

 fertility of the crossed offspring, of which fact evidence will 

 hereafter be given ; for this will lead to the mongrels increasing- 

 more rapidly than the pure parent-breeds. 



1 Communications to the Board of land/ 1S0S, p. 200. 



Agriculture, vol. i. p. 367. 3 < Saugethiere von Paraguay,' 1830, 



2 ' Eeview of Keports, North of Eng- s. 212. 



















