399 
fruit-eating birds, it ought to be possible to show that the 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 fruit-eating pigeons and, as this area lies on both sides of the equator, 
the annual changes of season must canse 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 Northern 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 Galoenas nicoharica, 
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 
given locality, as is true of Garpophaga hicolor, Garpophaga insularis, 
Galcenas nicoharica, 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 bii’ds 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 fcetida, 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 species, ofi 
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 
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