MIGRATION IN ITS BEARING ON LAMARCKISM II5 



surface of the ocean, but this affords no nesting place, while the 

 wastes of water which keep carnivorous mammals and reptiles 

 and other enemies of nesting birds from approaching the remote 

 and desolate rocks and sand-bars of the open ocean, are no ob- 

 stacle to them. These spots are so secure that birds born in 

 them are much more likely than those born on the shores of in- 

 habited lands to survive, so that it has come about that all the 

 modern members of these groups are descended from ances- 

 tors who shunned the dangerous nesting places, not because 

 acquired characters have become inherited, nor because their 

 feeding ground and their nesting places have been drawn apart 

 by geological changes, but because those which did not instinc- 

 tively seek safe places for the few eggs which are all that their 

 fitness for continuous and rapid flight permits have been extermi- 

 nated. These birds now gather from all parts of the ocean, on 

 the few widely scattered rocks and islands where their young are 

 safe, and the periodic assemblies of innumerable multitudes of 

 wandering sea-birds in their " rookeries " are true migrations, for 

 they are as regular as the almanac in the time of arrival and 

 departure, although their feeding ground is almost as extensive 

 as the ocean, and although the food-supply has nothing to do 

 with their movements, and although they do not reach the rook- 

 eries by a single path. 



In this case the needs of reproduction are the controlling influ- 

 ence, and the site of the rookery has been fixed by its safety ; and 

 while it is difficult to say how far the birds are guided by experi- 

 ence of the danger of other places, the well-known tameness of 

 sea-birds in their breeding places, and their apparent ignorance of 

 the existence of enemies, seem to show that they are quite uncon- 

 scious of the advantages of the chosen spot, and that they resort 

 to it automatically or naturally, since they owe their existence to 

 its isolation and its safety. 



Zoologists are far too ready to resort to the boundless fields 

 for speculation which geology affords, and Crotch has gravely sug- 

 gested that the migration of the lemmings, and their death in the 

 waters of the ocean, may be due to their efforts to reach the lost 

 Atlantis which their ancestors inhabited during the Miocene period ; 

 although this opinion has no better basis than the belief of Olaus 



