CHAP. XIX THE MADAGASCAR GROUP 437 



and multiply unchecked by the. at tacks of any more power- 

 ful animals, we can well understand that the wings, being 

 useless, would in time become almost aborted.^ It is also 

 not improbable that this process would be aided by 

 natural selection, because the use of wings might be 

 absolutely prejudicial to the birds in their new home. 

 Those that flew up into trees to roost, or tried to cross 

 over the mouths of rivers, might be blown out to sea and 

 destroyed, especially during the hurricanes which have 

 probably always more or less devastated the islands ; while 

 on the other hand the more bulky and short-winged 

 individuals, who took to sleeping on the ground in the forest, 

 would be preserved from such dangers, and perhaps also from 

 the attacks of birds of prey which may always have visited 

 the islands. But whether or no this was the mode by which 

 these singular birds acquired their actual form and 

 structure, it is perfectly certain that their existence and 

 development depended on complete isolation and on free- 

 dom from the attacks of enemies. We have no single 

 example of such defenceless birds having ever existed on 

 a continent at any geological period, whereas analogous 

 though totally distinct forms do exist in New Zealand, where 

 enemies are equally wanting. On the other hand, every 

 continent has always produced abundance of carnivora 

 adapted to prey upon the herbivorous animals inhabiting 



^ That the dodo is really a degradation from a higher type, and not a 

 direct development from some lower form of wingless bird, is shown by its 

 possessing a keeled sternum, though the keel is exceedingly reduced, being 

 only three-quarters of an inch deep in a length of seven inches. The most 

 terrestrial pigeon — the Didunculus of the Samoan Islands, has afar deeper 

 and better developed keel, showing that in the case of the dodo the degrada- 

 tion has been extreme. We have also analogous examples in other extinct 

 birds of the same group of islands, such as the flightless Kails— Aphan- 

 apteryx of Mauritius and Erythromachus of Rodriguez, as well as the 

 large parrot — Lophopsittacus of Mauritius, and the Night Heron, 

 Nycticorax iiugcwephala of Rodriguez, the last two birds probably having 

 been able to fly a little. The commencement of the same process is to be 

 seen in the peculiar dove of the Seychelles, Turtur rostratus, which, as 

 Mr. Edward Newton has shown, has much shorter wings than its close 

 ally, T. piduratus, of Madagascar. For a full and interesting account of 

 these and other recently extinct birds see Professor Newton's article on 

 ** Fossil Birds" in the Encydopccdia Britannica, ninth edition, vol. iii., 

 p. 732 ; and that on ** The Extinct Birds of Rodriguez,"' by Dr. A. Giinther 

 and Mr. E. Newton, in the Royal Society's volume on the Transit of Venus 

 Expedition. 



