INTRODUCTION. XUl 



precise facts and ideas, based upon realities in such 

 a manner as to enable them to seize upon their true 

 relations and their most general consequences ? 



Would not the habits thus based upon a metho- 

 dical system find constant application even in our 

 daily lives ? Considered from this point of view, 

 there is no science that can replace the natural 

 sciences generally, and zoology more particularly. 



I have thus endeavoured to indicate the ideas by 

 which I have been influenced in the composition of 

 the present work, and it now only remains for me 

 to say a few words regarding the mode of its exe- 

 cution. 



In addressing myself to the habitual readers of 

 the Revue des deux mondes I was speaking to an 

 educated and intelligent class, who, however, have 

 very little familiarity with the natural sciences. I 

 was, therefore, obliged to proceed with some reserve, 

 more especially at the beginning, and hence I almost 

 always avoided entering into technical details, limit- 

 ing myself almost exclusively to general questions. 

 In this manner I often sought to imitate the phy- 

 sician who envelopes in honey the unsavoury medi- 

 cine which might otherwise be repulsive to his 

 patient, and hence I have interwoven descriptive or 

 historical details in nearly all the chapters of the 

 work. 



Having yielded thus far to the necessities of the 

 case, I devoted myself so much the more earnestly 



