318 THE CROSSING, &C, OF CATTLE, ET At. 



posteriori, by actual observation; and a priori, from 

 the loss of interstitial tissue, necessarily involved; from 

 the fact, that many organs must be measurably im- 

 paired, in function, when their size is reduced; and, 

 from the fact, that, when dissimilarly developed ani- 

 mals, of a species, are crossed, increase in size results, 

 and when disproportionately developed animals are 

 interbred, decrease in size is occasioned. The small 

 size of many Horses (Ponies, &c), is due to their close 

 interbreeding, which was incompetent, by reason of the 

 animals' little disproportion, to work much loss of fer- 

 tility, or of constitutional vigor; but, which elicited the 

 evil of disproportion, chiefly by means of reduction in 

 size. This view is confirmed by the fact, that, when a 

 small number of animals, much disproportionately de- 

 veloped, are restricted within a narrow range, such 

 as an island, or a valley enclosed by impassable moun- 

 tains, thus necessitating their interbreeding, the ani- 

 mals die out; but, when animals but little dispro- 

 portionately developed (such as Horses), are so con- 

 fined, and constrained to interbreed, they do not so die 

 out, but become, instead, much reduced in size, — the t 

 reduction being caused by the little disproportion 

 which is insufficient much to affect their fertility and 

 vigor. Jersey and Alderney breeds are also instances 

 of the operation of this principle. 



They are too little disproportionately developed to 

 have entailed upon them the evils of much lessened 

 fertility and of much lessened constitutional vigor, from 

 interbreeding not very close ; but the defects in struc- 

 ture which they have, entail, instead, reduction in size. 



