ROUTES OF MIGRATION. 95 



All these facts tend to show that Migration Routes, 

 broadly speaking, are continuous, and that it is only 

 under such a condition that Migration ever became 

 a possibility, or even had an existence. Widely 

 disconnected sea routes of migration are as rare as 

 discontinuous areas of distribution, and in many 

 cases not only terminate in emigration, but ulti- 

 mately in segregation and the establishment of 

 new races. Had there been no means of slowly 

 acquiring the habit in past ages by easy sea 

 passages, or by a continuous land area from north 

 to south or from east to west, had broad expanses 

 of ocean barred the way of retreating birds during 

 periods of climatal change, all the ancestors of our 

 northern avifauna would either have perished or 

 reached southern lands nev^er to return ; or if some 

 did succeed in returning they w^ould have come as 

 emigrants, and migration would have been unknown ! 

 Tested by such facts as are here adduced, it w^ould 

 seem that the migration from the Antarctic regions, 

 which in a previous chapter I have suggested took 

 place on a very important scale in past ages, must 

 be an erroneous conclusion. But the difficulty is 

 more imaginary than real. Even at the present 

 day most of the vast ocean space between the now 

 glaciated Antarctic continent and the two great land 

 masses of America and Asia may be so bridged by 

 islands that the continuous water passage does not 

 exceed 500 miles, except to the south of New 

 Zealand (700 miles), and to the south of Africa 

 (1500 miles). From this we may naturally infer 



