SUMMARY AND CONCLUSION 293 



brief allusion to Irruptic Emigrations, showing their 

 abnormal character and their failure in the majority of 

 instances to extend distribution. 



Among the more important points dealt with in the 

 present volume may be mentioned the following : — 



I. A new Law of Dispersal. 



II. Polar Dispersal — from either Pole — a myth. 



III. Glacial Epochs exterminated Life ; did not cause 

 Emigration or " retreat " from adverse climatic cooiditions. 



IV. The sources or Range Bases whence the British 

 Post-Glacial Avifauna has been derived. 



V. Past geographical Mutations have been shown to 

 be in harmony with the present geographical Distribution 

 of Species. 



VI. Endemic island species are never produced on 

 routes of migration of closely-allied parental species. 



VII. Emigration or Range-extension is rarely made 

 across wide water areas ; but Migration, once established 

 across such, when the land v/as continuous or nearly so, 

 is only arrested by extermination. 



VIII. The origin of the West to East Migration across 

 the North Sea. 



IX. Additional light has also, I believe, been thrown 

 on the Migration Routes of Birds. 



X. Internal Migrations, Local Movement, Irruptic 

 Emigration, and Recent Emigration have all been treated 

 from what I believe to be new points of view. 



XI. A short comprehensive account of the Spring 

 and Autumn Aspects of Migration across the British 

 Archipelago. 



XII. The important bearing of the new Law of Dis- 

 persal on the Distribution of Floras. 



