On the general geographical distribution of the members of the class Aves.

Sclater defined and named six zoological regions: the Palaearctic, Aethiopian, Indian, Australasian, Nearctic and Neotropical. With some name revision (Afrotropic for Aethiopian, and Indomalayan for Indian,) these zoogeographic regions are still in use. Digital facsimile from the Linnean Society at this link.