vi PREFACE. 



past history of the earth as revealed by geology, and obtain 

 some indications of the existence of those ancient lands which 

 now lie buried beneath the ocean, and have left us nothing but 

 these living records of their former existence." 



The detailed study of several groups of the birds and insects 

 collected by myself in the East, brought prominently before me 

 some of the curious problems of Geographical Distribution; 

 but I should hardly have ventured to treat the whole subject, 

 had it not been for the kind encouragement of Mr. Darwin and 

 Professor Newton, who, about six years ago, both suggested that 

 I should undertake the task. I accordingly set to work ; but 

 soon became discouraged by the great dearth of materials in 

 many groups, the absence of general systematic works, and the 

 excessive confusion that pervaded the classification. Neither 

 was it easy to decide on any satisfactory method of treating 

 the subject. ; During the next two years, however, several im- 

 portant catalogues and systematic treatises appeared, which 

 induced me to resume my work ; and during the last three years 

 it has occupied a large portion of my time. 



After much consideration, and some abortive trials, an outline 

 plan of the book was matured ; and as this is, so far as I am 

 aware, quite novel, it will be well to give a few of the reasons 

 for adopting it. 



Most of the previous writings on Geographical Distribution 

 appeared to me to be unsatisfactory, because they drew their 

 conclusions from a more or less extensive selection of facts ; and 

 did not clearly separate groups of facts of unequal value, or 

 those relating to groups of animals of unequal rank. As an 

 example of what is meant, I may refer to Mr. Andrew Murray's 

 large and valuable work on the Geographical Distribution of 

 Mammalia, in which an immense number of coloured maps are 



