RECENSIO CONTRADICTORIA. 



king instances, that in the mind of some writers thousands, even hun- 

 dress of thousands of years were necessary to establish Migration, 

 whereas another is satisfied with merely 2000 years ! 



hi looking back to the time of Emperor Frederic (XIII. century) 

 we have a good measure for the valuation of many facts, as well as 

 for the progress in our knowledge of Bird-Migration. „Only per- 

 fectly feathered individuals migrate" - „not all Birds are Birds of 

 Passage", and chiefly section 14: „the bird at the head of the proces- 

 sion < is relieved, because he has the hardest work, having to consider 

 also dangers etc . . ." This proves that the Emperor must have had on 

 idea of the work accomplished by the leading bird and that his opinion 

 on this subject is much closer to the results of modern knowledge, 

 than that of some ornithologists, even of modern time, who still cannot 

 do without the idea of leadership. 



.«&. 



^ 



^ 



63 eai 



