NO MAD re MIGRATION. 165 



as possible, even during the periods of greatest 

 glacial intensity, seems very probable ; just as round 

 the margin of the glaciated South Pole we now find 

 a few birds — last relics, we are compelled to regard 

 them, of that rich and abundant Antarctic avifauna 

 that dwelt round the Southern Pole in long past 

 Eocene ages, and which was scattered north pro- 

 bably by a Post-Eocene Glacial Epoch. From 

 Namadic Migration we can gradually trace the 

 movement into short but Regular Passage ; and 

 thence through every gradation to those long 

 extended flights which we justly look upon with 

 admiration and with wonder. These nomadic 

 migrations represent incipient migration in the past, 

 which never developed in these species or their 

 ancestors to any greater extent than what we now 

 witness ; but, as we have already seen in a vast 

 number, in the great majority of others it gradually 

 became a function of the highest importance. 



It is also worthy of remark, that the species per- 

 forming the shortest regular migrations are closely 

 allied to these nomadic migrants. There are few, 

 if any, wide-ranging migrants among the Crows 

 (Corvid.-e), or Finches (FRiNGiLLm.E), Ducks (Ana- 

 Tm.E), or Auks ( Algid. ^), or Gulls (Larid.^), unless 

 belonging to different genera, which indicates more 

 distant relationship. This fact, so far as it goes, is 

 one very good reason for placing such thoroughly 

 Arctic and isolated species in genera to themselves, 

 in spite of the remonstrances of some naturalists, 

 who always seem to think that a genus cannot be 



