408 



ISLAND LIFE. 



[part II, 



reached the group by means of intervening islands afterwards 

 submerged, and to have thenceforth remained to increase and 

 multiply unchecked by the attacks of any more powerful 

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

 would in time become almost aborted.^ It is also not im- 

 probable 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 pre- 

 served 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 freedom from the attacks of enemies. We 

 have iro single example of such defenceless birds having ever 

 existed on a continent at any geological period, whereas analogous 



1 That the dodo is really an abortion from a more perfect 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 a far deeper 

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

 degradation has been extreme. We have also analogous examples in other 

 extinct birds of the same group of islands, such as the flightless Rails — ■ 

 Aphanapteryx of Mauritius and Erythromachus of Rodriguez, as well as 

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

 Nycticorax megacephala 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. jjicturatus, 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 Encydopcedia 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. 



