THESES FROM LITERATURE. 



14. Birds act with a purpose and therefore instinctively. 



15. The front of Migration corresponds to the breeding region. 

 Martorelli, Giacinto, Prof.; „Le mute regressive degl'lJcelli migranti 



etc." 1892.* 



1. The ease with which birds are able to change locality, for 

 which they are predestined in consequence of their bodily cons- 

 titution, was the reason for Migration, which became regular 

 and hereditary. 



2. The fact that refrigeration in the Arctic regions lasted for cen- 

 turies or a change caused through special glacial period had no 

 doubt a powerful effect upon the distribution and differenti- 

 ation of Birds. 



3. Temperature has no decisive influence upon Migration: the latter 

 is based upon the want of food and safety. 



4. The number of species actually known as migratory Birds is so 

 large, that Migration may be considered rather a rule than an 

 exception. 



5. Migration is not constant and is not uniform even with indivi- 

 duals of the same species. 



6. The oscillations in Migration are in close connexion with the 

 habits of birds and the localities haunted by them. 



7. The colour in the majority of migratory Birds at least in 

 our Hemisphere — is either little different or becomes more 

 striking only after arrival at the breeding places. 



8. If there is a marked difference in colours between the sexes 

 of the same species, the colour of mature males before lea- 

 ving for winter-quarters is likely to be confused with that of 

 immature males. 



9. Birds breeding in one Hemisphere do not breed in the other, 

 but |3ass over to the latter in the second summer. 



• A diligent compilation. 



120 46 ita 



