326 THE CROSSING, &C, OF CATTLE, ET AL. 



attended with the greatest increase of fertility, because 

 the many widely divergent varieties of these species, 

 necessarily imply great disproportionate development, 

 of each variety. They are, therefore, extremely sus- 

 ceptible to improvement, because they lack so many 

 characters ; and, when two varieties, of one of those 

 species, cross, there results, to the offspring, the acces- 

 sion of some important character which one of the 

 parents lacked. 



The different breeds of Cattle, and of Sheep, on the 

 other hand, approximate closely to the sum of all the 

 characters of their respective species. There is, there- 

 fore, comparatively little, to be gained, by any one of 

 these breeds, from a cross. The positive differences, 

 distinguishing the other varieties, are very few, very 

 slight, and of comparatively little importance. 



Strikingly in harmony with this interpretation, is 

 the fact, that the more highly-bred the Pigeons are, 

 the greater, is the gain, from a cross. The reason is, 

 because the more highly-bred the breeds are, the more 

 divergent they are ; the more distinct they are ; and 

 the greater is the need for each to possess the charac- , 

 ters which, in the others, have been pushed to an ex- 

 treme point. 



Equally congruous, is the converse fact, namely, 

 that the more highly-bred, generally, that the breeds 

 of Cattle and of Sheep, are, the less is the gain from 

 the crossing of two varieties of one of the species. This 

 is because, the more highly-bred the breeds of Cattle 

 and of Sheep, become, the more, generally, do they all 

 converge to the full and proportionate development of 



