OF THE CLASS MAMMALIA. 243 



has its purity secured by authentic legal attestations, during 

 a series of four ages, and the known genealogy of several 

 of these fine animals extends to two thousand years. The 

 English race-horse owes its qualities to a mixture of the Arab 

 stallion with the indigenous mares of England ; hence its sta- 

 ture and astonishing rapidity. The abundance and quality 

 of the food, the nature of the climate, the daily cares bestowed 

 on the horse, influence the race much more than is generally 

 supposed : as a proof of this, we may notice the rapidity with 

 which the finest English horses degenerate in certain locali- 

 ties, as in the studs of Kopschan on the borders of Moravia. 

 .But the same fact may be observed nearer home. If two 

 colts of the same breed, of Lorraine for example, be placed, 

 one in Flanders the other in Normandy, instead of retaining 

 their resemblance to each other, they will at five years resem- 

 ble horses of different breeds : the one will grow up a coach - 

 horse, light and elegant; the other an enormous animal, 

 hardly able to trot, but equal to the draught of the heaviest 

 loads. Where nourishment abounds, there the size and 

 weight of the horse increase; opposite circumstances are 

 attended with other results. Fed on strong humid pastures, 

 the horse becomes heavy, and his form and hair coarse ; on 

 light soils, and especially if grain be added to his ordinary 

 food, his form becomes light and elegant : finally, the careful 

 grooming bestowed on the English horse contributes to 

 improve his form, and especially the fineness of his limbs. 

 Thus it happens, as in the dog, that varieties may be so 

 multiplied as to make it appear that they must have sprung 

 from more than one species : nevertheless, all these modifica- 

 tions have their limits, beyond which nature will not or 

 cannot go : they never destroy the distinctive characters of 

 zoological species.* 



409. Classification of the Mammalia. There exist, 

 as we have seen, considerable differences amongst the mam- 

 malia, and these modifications of structure serve as the 

 basis for the division of the class into groups of an inferior 

 rank, called orders. Most of these groups are so distinct as 

 to admit of no doubt in respect of their limits ; they consti- 

 tute, in fact, natural divisions ; but in others the line of 

 demarcation is by no means so distinct. Thus a mammal 



* Experiments made in this country have led to entirely different results. 

 The various breeds of horses, cattle, and sheep remain unaltered, on whatever 

 pastures they may be fed. R. K. 



