Vlll PKEFACE. 



entirely out of date, and in no way represents the present 

 status of the science. 



The subject of geographical and geological distribution is 

 so vast that no full treatment of it could be expected in the 

 limited number of pages set apart for it in the present work. 

 The author has, therefore, been obliged to omit, or at least 

 largely ignore, the consideration of some of the less impor- 

 tant animal groups, and, while recognising the deficiencies 

 resulting from such omission, trusts that it will not detract 

 much from the general usefulness of the publication. The 

 plan of treatment followed in the early part of the book 

 (geographical distribution) is largely that so admirably un- 

 folded by Mr. Wallace, to whom, for the constant use of his 

 works, the author is under great obligations. He also wishes 

 to express his special indebtedness to the pioneer workers in 

 this field, Schmarda and Murray, whose writings have laid 

 the foundation of much of our existing knowledge in the 

 premises. No special mention need be made of the numer- 

 ous other authors who have contributed more or less exten- 

 sively to the subject under consideration, and whose works 

 have aided in the preparation of the present volume ; to those, 

 collectively, the author likewise desires to acknowledge his 

 indebtedness. 



A few words need be said in relation to the zoogeographical 

 regions that are recognised in this work, which differ essen- 

 tially from those generally adopted by naturalists. The rea- 

 sons for uniting the "Nearctic" and " Palaearctic " regions 

 of zoogeographers into a single realm, designated, in accord- 

 ance with a suggestion by Professor Alfred Newton, of Cam- 

 bridge, the " Holarctic," are fully set forth in my paper " On 

 the Value of the Nearctic as one of the Primary Zoological 

 Regions," published in the " Proceedings of the Academy of 

 Natural Sciences of Philadelphia," for December, 1882. Ob- 



