PREFACE TO THE FIRST EDITION 



The present volume is the result of four years' additional 

 thought and research on the lines laid down in my 

 Geographical DistHhution of Animals, and may be con- 

 sidered as a popular supplement to and completion of that 

 work. 



It is, however, at the same time a complete work in 

 itself : and, from the mode of treatment adopted, it will, I 

 hope, be well calculated to bring before the intelligent 

 reader the wide scope and varied interest of this branch of 

 natural history. Although some of the earlier chapters 

 deal with the same questions as my former volumes, they 

 are here treated from a different point of view ; and as the 

 discussion of them is more elementary and at the same 

 time tolerably full, it is hoped that they will prove both 

 instructive and interesting. The plan of my larger work 

 required that genera only should be taken account of; in 

 the present volume I often discuss the distribution of 

 species, and this will help to render the work more intelli- 

 gible to the unscientific reader. 



The full statement of the scope and object of the present 

 essay given in the " Introductory " chapter, together with 

 the " Summary " of the whole work and the general view 

 of the more important arguments given in the " Conclu- 

 sion,'' render it unnecessary for me to offer any further 

 remarks on these points. I may, however, state 



