14 



INTRODUCTION. 



because it collects under one point of view, and gives a rational 

 explanation of, many apparently independent classes of facts. 4 



4 In treating the several subjects in- 

 cluded in the present and succeeding 

 works I have continually been led to 

 ask for information from many zoolo- 

 gists, botanists, geologists, breeders of 

 animals, and horticulturists, and I have 

 invariably received from them the most 

 generous assistance. Without such aid 

 I could have effected little. I have 

 repeatedly applied for information and 

 specimens to foreigners, and to British 



merchants and officers of the Govern- 

 ment residing in distant lands, and, with 

 the rarest exceptions, I have received 

 prompt, open-handed, and valuable as- 

 sistance. I cannot express too strongly 

 my obligations to the many persons 

 who have assisted me, and who, I am 

 convinced, would be equally willing 

 to assist others in any scientific investi- 

 gation; 



