258 CLASS MAMMALIA. 



may be permitted to single out any instance for eulogium 

 in preference to others), and one indispensably necessary 

 for the preservation of animal existence. In fact, in the 

 very earliest steps which are made in the study of living 

 beings, this grand truth must be felt and acknowledged. 

 It is to this faculty that all individual, perhaps too, all spe- 

 cific varieties are owing, and most certainly all the races 

 of our domestic animals. Without it, life itself would 

 ere long be extinct from the surface of the earth. Were it 

 withdrawn, all nature would speedily exhibit the most de- 

 plorable spectacle of disease, decay, decrepitude and death. 

 This cannot be doubted for an instant, when we consider 

 the effect which the most feeble of these modifying causes 

 will produce upon animals not properly prepared to resist 

 them. The natives of hot climates seldom pass with impu- 

 nity into colder regions, unless the change be carried on by 

 almost imperceptible gradations. And the case is the same 

 with those which pass from Northern countries into torrid 

 or even into temperate latitudes. 



Notwithstanding the high importance of this law of na- 

 ture, it has not yet been made the subject of any particular 

 study. Every day we see doubts started on the characters 

 of species and varieties, and we are in the most profound ig- 

 norance of the effects proper to each modifying cause, as 

 we are also respecting the nature of these causes them- 

 selves. This is a branch of science totally neglected, al- 

 though it might conduct to the most curious and useful 

 discoveries. The transformation of the rough covering of the 

 Argali {Oms Ammon, Gm.) into the soft and beautiful fleece of 

 the Merinos, the domesticity of the Dog, the subjection of the 

 Horse, a thousand other phenomena of this description are 

 incontestably verified, yet no attempt is made to investigate 

 their producing-causes. But if on the one side it is im- 

 portant to make experimental researches on this point, it 

 is no less so to ascertain the varieties which nature herself 



