1891.] D. Prain— T^e Vegetation of the Coco Group. 3'99f 



fruit-eating birds, it ouglit to be possible to show that tbe known migra- 

 tions of these creatures sufficiently explain their distribution. For all 

 the species that occur in the Malay Archipelago this is extremely easy 

 to do. The western half of the Malay Archipelago is particularly rich 

 in fi'uit-eating pigeons and, as this area lies on both sides of the equator, 

 the annual changes of season must cause the fruit-eating species, follow- 

 ing the fruits on which they feed as these become mature, to oscillate 

 from side to side of the equator. The same condition will ensure further 

 migration from Southern Malaya to North Australia and vice versa on 

 the one hand, and from JSTorthern Malaya to the Nicobars and Andamans 

 and vice versa on the other. It is not necessary to suppose that any 

 particular fruit-eating bird must range from one end to the other of 

 the area here considered, though some species, like Galcenas nicobarica, 

 which extends from these islands to New Guinea, nearly or altogether 

 do so ; it is sufficient to know that such birds are seasonal visitants in 

 any given locality, as is true of Garpophaga bicolor, Garpophaga insularis, 

 Galcenas nicobarica, and many other species in those very islands ; the 

 region depleted of one set of species by the migration of these towards 

 the north is filled with individuals representing another set coming 

 from an area still further south. By the necessary over-lapping of 

 the ranges of migration of different birds a continuous chain of dispersal 

 is kept up and, even if Malayan birds never go further north than 

 these islands, the process is continued by the arrival from and departure 

 to the opposite point of the compass, of Indo-Chinese species ; it is 

 therefore not surprising to find that, where the climatic conditions still 

 continue favourable, the same bird-distributed species of Phanerogams 

 extend from North Australia through all the intervening areas to 

 Southern China. This being so, the appearance of the same species in 

 India and in Malaya, which is the case in 33 species, or 58 per cent., of 

 the group, is simply explained. Certain species of birds, instead of 

 only passing southward from China to Indo-China, pass also south- 

 westward to the Eastern Himalaya or to the Assam valley, from whence 

 these, or other, species of birds carry the seeds of the plants in question 

 still further south-westward into peninsular India. This may explain 

 also why certain species, like Pcederia foetida, extend from Malaya 

 northwards to Indo-China on the eastern line of migration, but on 

 the western extend only southward to the Eastern Himalaya and not 

 into India ; the species of birds that eat their fruits may perhaps not 

 migrate on the more western line of migration further south than the 

 Himalayan slopes. The same reasoning applies to those speqies, of 

 which there are 3, or about 5 per cent., that extend to Southern India 

 on the western line of migration but do not go as far as Malaya on the 



