THESES FROM LITERATURE. 



Severtzow N. Dr.: „Etudes siir le passage des oiseaux dans I'Asie- 

 Centrale, 1875. 



1 . Every species travels along its own route. 



2. On the way Birds stop at quite inappropriate places. 



3. Migration-routes are strips of land, where Birds appear in greater 

 numbers than in the intervening tracts. 



4. All routes are characterized by crowds of first passers whicii 

 neither nidificate nor hibernate. 



5. Alpine Birds do not migrate, but pass into the valleys. 



6. East of Khanghai the entire passage is directed to China. 



7. The migration-routes, which are close together in Central-Asia, 

 branch off in the north and also cross each other. 



Wallace, R A : „Die geographische Verbreitung der Thiere" 1876. 



1 . Weather has no essential influence on Migration 



2. The oscillation in the spring-migration amounts only to 14 days. 



3. Old Birds wander farther south than young ones. 



4. Migration dates from a period, when the Mediterranean Sea did 

 not exist. 



5. The Mediterranean is passed only at certain points: Gibraltar, 

 Sicily, Malta, Ionian Islands. 



Weissmann, Aug : „Uber das Wandern der Vogel" Samml gem. 

 wissensch Vortrage, herausgegeben von Rud. Virchow und 

 Friedr. von Holzendorff. Berlin 1878. Scr. XIII, Heft 291. 



1. The nature of the phenomenon of Migration is already known. 



2. Birds of Migration are influenced by an impulse, w hicli originates 

 from passing (roving) — imperfect migration. 



3. Only such birds migrate as cannot exist without change of 

 place. 



4. Birds are taught to wander; troops migrate under the guidance 

 of old experienced Birds, which fly at the head of the procession. 



5. Birds follow distinct Migration-routes. These migration roads 

 arc the old routes by which they spread northward. 



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