essential, while isolation, or restriction to a limited area, plays an important part by keeping together those birds, or that race of birds, whose members show a tendency to disuse their wings. It will be seen that such combinations of circumstances will most naturally be found on islands whose geological history is such that they have had no connection with adjacent continents, or such a very ancient connection that they were not then peopled with beasts of prey, while subsequently their distance from other countries has prevented them from receiving such population by accident in recent times and has also retarded the arrival of man. [11] _The dingo, or native dog, is not forgotten, but, like man, it is a comparatively recent animal._ [12] _Note that in Tasmania, which is very near Australia, both in space and in the character of its animals, there are two carnivorous mammals, the Tasmanian "Wolf" and the Tasmanian Devil, and no flightless birds._ Once established, flightlessness and size play into one another's hands; the flightless bird has no limit placed on its size[13] while granted a food supply and immunity from man; the larger the bird the less the necessity for wings to escape from four-footed foes. So long as the climate was favorable and man absent, the big, clumsy bird might thrive, but upon the coming of man, or in the face of any unfavorable change of climate, he would be at a serious disadvantage and hence whenever either of these two factors has been brought to bear against them the feathered giants have vanished. [13] _While we do not know the limit of size to a flying creature, none has as yet been found whose wings would spread over twenty feet from tip to tip, and it is evident that wings larger than this would demand great strength for their manipulation._ _REFERENCES_ _There is a fine collection of mounted skeletons of various species of Moas in the Museum of Comparative Zoology at Cambridge, Mass., and another in the American Museum of Natural History, New York. A few _other skeletons and numerous bones are to be found in other institutions, but the author is not aware of any egg being in this country. Specimens of the AEpyornis are rare in this country, but Mr. Robert Gilfort, of Orange, N.J., is the possessor of a very fine egg. A number of eggs have been sold in London, the prices ranging from L200 down to L42, this last being much less than prices paid for eggs of the great auk. But then, the great auk is somewhat of a fad, and there are just enough eggs in existence to bring one into the market every little while. Besides, the number of eggs of the great auk is a fixed quantity, while no one knows how many more of AEpyornis remain to be discovered in the swamps of Madagascar. No specimens of the gigantic Patagonian birds are now in this country, but a fine example of one of the smaller forms, Pelycornis, including the only breast-bone yet found, is in the Museum of Princeton University._