XX INTEODUCTION. 



dispersal in my two volumes on the migration of birds. An introductory chapter 

 in a work like the present does not afford the necessary facilities for the discussion 

 of such a complicated question, but I hope shortly to elaborate my views in a 

 special volume devoted to the geographical history of avine life. It is sufficient 

 here to say that, in my opinion, all the available evidence tends to show that 

 Life is of equatorial origin, and tha/t from such a vast centre living forms have 

 drifted in strict accordance to law north and south towards the poles. That law, 

 briefly stated, is that species spread in the direction of the poles and towards 

 points of least resistance in the struggle for existence. Following Huxley to 

 some extent, I have divided the world into three realms. First, an Intertropical 

 or Primogsean realm, with northern and southern limits marked tentatively by 

 the tropics ; second, an Arctogsean or Northern realm, which embraces the 

 entire world north of the Tropic of Cancer ; third, a Notogsean or Southern 

 realm, which in like manner includes the entire world south of the Tropic of 

 Capricorn. We need scarcely have alluded to this law of dispersal in the present 

 volume, but the reader will find many instances of its application in the 

 geographical ranges of the various species dealt with in the following pages. 

 This is more especially the case when we come to treat with the various species 

 of "Waders — birds with extended areas of distribution in both the northern and 

 southern hemispheres. The reader will find that I have endeavoured to deal with 

 many problems of distribution in a manner opposed to the generally accepted 

 views of ornithologists. In many of these cases we are unfortunately without 

 sufficient data to furnish absolute proof of our contention, but we wait with every 

 confidence the exploration of the Antarctic and high Southern regions, and the 

 accumulation of additional facts relating to the habits and movements of certain 

 species in the Southern hemisphere, to support the views we hold on these 

 important questions. We will now proceed to glance in detail at the general 

 features of the geographical distribution of the several orders dealt with in the 

 present volume. 



Our first order consists of the Columbiformes or Pigeons, The Pigeons are 

 a widely distributed group, but the four hundred and seventy or so species that 

 compose it are very unequally dispersed, even in those warmer portions of the 

 globe that they chiefly affect. They are by far the least abundant in cold northern 

 latitudes, and perhaps reach their highest degree of development, and certainly 

 their preponderance in numbers, in the Australian region — an area, be it 

 remarked, abounding in islands and offering those faciHties for isolation so 

 favourable to the establishment of new species — the number of known species 

 therein nearly equalling those in all other parts of the world combined. The 

 Nearctic and Palaearctic regions are the poorest in species ; the Ethiopian region 

 comes next ; whilst the Oriental and Neotropical regions, next to the Australian 

 region, are nearly equal in their number of Columbine forms and abundantly 

 represented. The Pigeons belonging to the British genera, Columba and Turtur, 



