PREFACE 



The want of a small work dealing with the adaptations 

 and factors of animal life in a broad and connected 

 manner is my excuse for writing this book. In the 

 simplest form and with the least amount of descriptive 

 structural detail that I can compass, I have attempted 

 to describe the moving spectacle : its abundance and 

 variety, its modes of maintenance and of development, 

 the safeguards of its individual and racial welfare. 

 The evolutionary standpoint is adopted throughout, 

 and in developing the subject I have proceeded by 

 the use of three leading motives that differentiate 

 animals from plants — movement, the acquisition of 

 solid food, and the nervous control of response to 

 changing order. To have included the factors of 

 animal evolution, so far as they are known, would 

 have unduly swollen the volume, and partly on that 

 account, partly also because ol such excellent recent 

 accounts as those by J. A. Thomson (' Heredity,' 

 Progressive Sci. Scries : Murray) and by R. H. Lock 

 (' Heredity, Variation, and Evolution ' : Murray), I 

 have omitted consideration of them. 



