Migrations of North American Birds. 261 



able, when the contrary is the case, an intervening island may 

 be destitute of the species. Thus Cuba lacks several species 

 common to the Bahamas and to Jamaica. 



Professor Agassiz (Types of Mankind, 1854) has urged very 

 strongly the recognition of an Arctic and an Antarctic Region 

 or " realm " — a point in favour of which there is much to be said, 

 but which cannot be discussed in the present article. He also 

 anticipates Dr. Sclater in regard to some of his views ; but the 

 facts at command at the time did not allow him to define the 

 boundary lines of the regions with the same precision. Still 

 more recently Dr. Pelzeln (Reise der Novara, 1865) insists like- 

 wise upon an Antarctic Region. 



Proceeding, now, to the especial subject of the present article, 

 the mapping out of North America with reference to the geo- 

 graphical distribution and migrations of North American birds, 

 it may be premised that in the article above referred to, by 

 Professor Agassiz, in Nott and Gliddou^s ' Types of Mankind,' 

 we find the first attempt to mark off the zoological provinces of 

 the New World — and very successful, considering the insufficient 

 data accessible at the time. In 1859 ^ Dr. Leconte sketched 

 out their boundaries in North America with more precision, 

 having particular reference to the distribution of Coleopterous 

 insects. 



The subdivisions by Dr. Leconte of these provinces, as based 

 on the study of their Coleoptera, do not agree strictly with 

 those of the ornithological faunse, especially in the considerable 

 number of local areas which he has adopted. This difference is, 

 however, easily intelligible when we bear in mind the much 

 superior power of flight and innate tendency to migration of the 

 bird as compared with the insect, the distribution of reptiles 

 agreeing much better with his outline than that of birds. 



To present the general principles of distribution to which I 

 have been led by an examination of the large collection of 



* '' Coleoptera of Kansas and New Mexico," Dec, 1859, Smitlisonian 

 Contributions, vol. xi. 



I may also refer to incidental mention of the same law in a paper by 

 myself on the birds of Cape St. Lucas, in the ' Proceedings of the PhUad. 

 Academy ' for Nov. 8th 1859, p. 299. 



