xu 



PREFACE. 



VIII. As it is the aim of the Physical Philosopher to determine " what are the fewest 

 and simplest assumptions, which being granted, the whole existing order of nature would 

 result,"* so the aim of the Philosophic Naturalist should be to determine how small a 

 number of primitive types may be reasonably supposed to have given origin by the ordinary 

 course of "descent with modification " to the vast multitude of diversified forms that have 

 peopled the globe during the long succession of geological ages, and constitute its present 

 Fauna and Flora. 



* Mill's ' Logic/ 3rd edition, vol. i, p. 327. 



