PREFACE 



IN the present volume I have attempted to summarise and 

 complete my half- century of thought and work on the 

 Darwinian theory of evolution. In several directions I 

 have extended the scope and application of the theory, and 

 have shown that it is capable of explaining many of the 

 phenomena of living things hitherto thought to be beyond 

 its range. 



Among these are the detailed distribution of plants and 

 animals, which I have discussed at some length. It occupies 

 about one-fourth of the volume (Chapters II. to VI.), and 

 brings out certain facts and conclusions which I believe will 

 be of interest to all plant-lovers, and also be not without a 

 certain value to botanists. 



Next in importance are three chapters (X., XI., and XII.) 

 devoted to a general review of the Geological Record and a 

 discussion of the various problems arising out of it. Some 

 of the conclusions to which this examination leads us are, I 

 believe, both important and of much general interest. 



In Chapter VIII. I have endeavoured to show natural 

 selection actually at work in continually perfecting that 

 wonderful co-adaptation of the most diverse forms of life 

 which pervades all nature. Some little-known aspects of 

 bird-migration are here discussed, and proof is given of the 

 enormous importance of mosquitoes for the very existence 

 of a considerable proportion of our birds, including most of 

 our most favoured pets and songsters. This chapter will, I 

 think, have a special interest for every bird-lover. 



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