X PREFACE. 



those evidences of the power, wisdom, mid 

 ooodness of God, which are manifested in the 

 living creation. The ^scientific knowledge of 

 the phenomena of life, as they are exhibited 

 under the infinitely varied forms of organiza- 

 tion, constitutes what is usnally termed Phy- 

 siology ; a science of vast and almost bound- 

 less extent, since it comprehends within its 

 range all the animal and vegetable beings on 

 the globe. This ample field of inquiry has, of 

 late years, been cultivated with extraordinary 

 diligence and success by the naturalists of 

 every country ; and from their collective la- 

 bours there has now been amassed an immense 

 store of facts, and a rich harvest of valuable 

 discoveries. But in the execution of my task 

 this exuberance of materials was rather a 

 source of difficulty ; for it created the necessity 

 of more careful selection, and of a more ex- 

 tended plan. 



In conformity with the original purpose of 

 the work, which I have all along endeavoured 

 to keep steadily in view, I have excluded from 

 it all those particulars of the natural history 

 both of animals and of plants, and all descrip- 

 tion of tliose structures, of which the relation 

 to final causes cannot be distinctly traced ; 



