it from both the adjacent regions. More evidence in the same direction will be found in the Second Part of this work, in which the extinct faunas of the several regions are discussed. A confirmation of the general views here set forth, as to the distinctness and approximate equivalence of the six regions, is to be found in the fact, that if any two or more of them are combined they themselves become divisions of the next lower rank, or "sub-regions;"--and these will be very much more important, both zoologically and geographically, than the subdivisions of the remaining regions. It is admitted then that these six regions are by no means of precisely equal rank, and that some of them are far more isolated and better characterized than others; but it is maintained that, looked at from every point of view, they are more equal in rank than any others that can be formed; while in geographical equality, compactness of area, and facility of definition, they are beyond all comparison better than any others that have yet been proposed for the purpose of facilitating the study of geographical distribution. They may be arranged and grouped as follows, so as to exhibit their various relations and affinities. Regions. { NEOTROPICAL Austral zone Notogæa. Neogæa { { NEARCTIC } } } Boreal zone } { PALÆARCTIC } } { } Arctogæa. { ETHIOPIAN } } Palæogæa { } Palæotropical zone } { ORIENTAL } } { { AUSTRALIAN Austral zone Notogæa. The above table shows the regions placed in the order followed in the Fourth Part of this work, and the reasons for which are {67}explained in Chapter IX. As a matter of convenience, and for other reasons adduced in the same chapter, the detailed exposition of the geographical distribution of the animals of the several regions in Part III. commences with the Palæarctic and terminates with the Nearctic region.