PREFACE 



THESE outlines of the distribution of animals 

 deal with a rather young branch of science. 

 An attempt has therefore been made to sketch its 

 rapid growth from small beginnings until it has become 

 boundless, because the interpretation of at first seem- 

 ingly simple facts in the domain of the zoologist, 

 had soon to enlist the help of well-nigh all the 

 other branches of Natural Science. The subject of 

 geographical distribution is the dispersal of life, the 

 greatest mystery of all, in space and time. The key 

 to the present lies in the past. 



The historical and introductory chapter is followed 

 by a few sketches of the home, as most intensified 

 kinds of which have been selected tropical forests, 

 deserts and high mountains with their various effects 

 of climate and the interdependence of animal and 

 plant life. Next come some short chapters on the 

 modes, means and rates of spreading ; and as one of 

 its main causes is the natural increase in numbers, 

 a few tentative remarks on numbers of species and 

 individuals, on rich and scanty faunas and kindred 

 questions have been added. Last, not least, given 

 the creatures, their home requirements and their 

 need to wander, the majority of them could not have 

 attained their present distribution, and the various 

 countries could not have got their present mixed 

 faunas, unless the map of the world had undergone 



