vi PREFACE 



possible results of future discoveries." To find explanation of the 

 facts of distribution under the current theories has always 

 seemed a very hopeless task, and any hypothesis that offers a 

 way out should at least receive attention. No hypothesis can, 

 after all, alter the facts, though it may show ways in which to 

 accumulate new ones. 



In the second part of the book, I have pushed my hypothesis 

 to what seem to me its logical conclusions, conclusions which 

 are sometimes subversive of received opinions. To be compelled 

 to re-examine the bases upon which those opinions are founded 

 will do science no injury, however. 



While the defects of the book are my own. I owe what is good 

 in it very largely to the constant help, advice, and criticism of 

 many friends, among whom I would specially mention Dr Hugo 

 de Vries, Dr H. B. Guppy, Mrs E. M. Reid, and Prof. James 

 Small, all of whom have also contributed chapters to the work. 

 To these four I must add my friend Mr G. Udny Yule, to whose 

 trained mathematical skill I owe much useful help and criticism. 

 Prof. J. Stanley Gardiner has helped me very greatly in the work 

 upon animals. In particular he was so kind as to obtain for me 

 the help of Dr Hugh Scott, who spent hours with me in counting 

 beetles, Mr E. Meyrick, F.R.S., who gave me figures for dis- 

 tribution of Micro-Iepidoptera, Mr G. C. Robson, and Dr W. T. 

 Caiman, F.R.S. To the criticism of Prof. E. S. Prior, A.R.A., I 

 largely owe the present simplified form of the book, and its 

 freedom from technical terms; he was also so kind as to obtain 

 for me the aid of Dr W. D, Lang. References to literature, and 

 other valuable help, I owe to Sir David Prain and Mr S. A. Skan 

 at Kew, Mr G. Goode, ]\I.A,, at the University Librarj^ IVIiss 

 Taylor at the Balfour Library, and others, whilst I am also 

 deeply indebted for help and criticism to (the late) Dr E. A. N. 

 Arber, Mrs Agnes Arber, Prof. Margaret Benson, ^Ir E. Breakwell, 

 Dr W. B. Brierley, Dr N. L. Britton, Dr J. Brownlee, Mr J. Burtt- 

 Davy, Dr L. Cockayne, (the late) Mr R. \V. Davie, Mr C. E. 

 Foweraker, Mr E. G. Gallop, Prof. R. Ruggles Gates, Dr B. 

 Daydon Jackson, (the late) Dr A. Lofgren, Dr D. T. MacDougal, 

 Dr J. H. Maiden, Miss E. R. Saunders, Dr D. H. Scott, Prof. 

 A. C. Seward, Mr A. M. Smith, Dr Norman Taylor, Dr R. J. 



