The geographical distribution of animals, with a study of the relations ...

;chap, xni.] THE AUSTRALIAN REGION. 39$know they have in the north. Perhaps a more important considerationis, that Didelphys is a family type unknown in Australia; and this implies that the point of common origin is veryremote in geological time. But the most conclusive fact is thatin the Eocene and Miocene periods this very family, Didelphyidse,existed in Europe, while it only appeared in Americain the Post-pliocene or perhaps the Pliocene period ; so that itis really an Old-World group, which, though long since extinctin its birthplace, has survived in America, to which country itis a comparatively recent emigrant. Primeval forms of marsupialswe know abounded in Europe during much of the Secondaryepoch, and no doubt supplied Australia with the ancestors ofthe present fauna. It is clear, therefore, that in this ease thereis not a particle of evidence for any former union betweenAustralia and South America ; while it is almost demonstratedthat both derived their marsupials from a common source in thenorthern hemisphere.Birds offer us more numerous but less clearly defined cases ofthis kind. Among Passeres, the wonderful lyre bird (Menura)is believed by some ornithologists to be decidedly allied to theSouth American Pteroptochidae, while others maintain thatit is altogether peculiar, and has no such affinity. The AustralianPachycephalia? have also been supposed to find theirnearest allies in the American Vireonida?, but this is, perhaps,equally problematical. That the mound-makers (Megapodiidse)of the Australian region are more nearly allied to the SouthAmerican curassows ^Cracidse) than to any other family, is perhapsbetter established ; but if proved, it is probably due, as inthe case of the marsupials, to the survival of an ancient andonce wide-spread type, and thus lends no support to the theoryof a land connection between the two regions. A recent author,Professor Garrod, classes Phaps and other Australian genera ofpigeons along with Zenaida and allied South American formsbut here again the affinity, if it exists, is so remote that the explanationalready given will suffice to account for it. Thereremain only the penguins of the genus Eudyptes ; and thesehave almost certainly passed from one region to the other, but