INTRODUCTION. 21 



power of maintaining itself in its original purity of form 

 and character *°, when such animated branch is not sub- 

 jected to the various physical and moral agencies re- 

 sulting from change of climate, restraint, and artificial 

 food. But it admits of as ready proof, and it has long 

 been observed by philosophers, that the same agen- 

 cies, arbitrarily imposed, possess a considerable modi- 

 fying power over the organization of animal bodies. 

 Of these agents, climate and domestication are the most 

 powerful. Climate, it is well known, has a great influ- 

 ence over all the living bodies placed under it : to its 

 operations on mankind we are to attribute the two op- 

 posite extremes of white and black races ; while extra- 

 tropical shades, ranging between these, as they ap- 

 proach to or recede from the sun's rays, confirm the 

 assumption. Within the tropics, almost all animal mat- 

 ter is distinguished by the strength and depth of its ex- 

 ternal hues ; whereas a blanching or whitening eff'ect is 

 produced, on the same matter, as it approaches the 

 poles. The Siberian roe, the varying hare, the varie- 

 ties of grous and partridge, even the diminutive mouse, 

 and, in fact, almost all the wild animals of high north- 

 ern latitudes, become lighter as winter approaches; 



«° Mr. Lawrence, in his scientific Lectures on Comparative Ana- 

 tomy (to which I am proud to own many obligations), observes, that 

 this inherent tendency to preserve the original form and character 

 " is illustrated by the zoological descriptions of Aristotle, which, 

 " although composed twenty-two centuries ago, yet apply, in all 

 " points, to the individuals of the present time ; and also, by all the 

 " works of art handed down to us from antiquity, in the form of 

 " statues, paintings, mummies, &c." It may be added, that, in the 

 human race, a similar tendency is observed. The Jewish or Cau- 

 cassian face has never altered, although spread over the globe ; and 

 the same may be remarked of Gipsies, who are generally considered 

 as descendants from the Egyptians. 



