393 
there all occur in India and ludo-China also, while two that occur in 
India and Indo-China but do not occur in Malaya must have been intro¬ 
duced from the north. This being the case the probability is that the 
others have mainly been introduced from the same direction, a cir¬ 
cumstance quite in accordance with expectation, since it is from the north 
that the stream of migration of marsh- and water-birds annually flows. 
Daring our visits to the islands snipe were found in the meadow near 
the lake on Great Coco, while teal and other water-birds frequented the 
lake itself and abounded in the lagoon on Little Coco. 
Table XX. Analysis of distribution of Marsh a 7 id Aquatic species. 
Present in both Hemispheres :— . y 
Cosmopolitan in the tropics:.. 
Nearly cosmopolitan (absent from Polynesia) . y., , i 
Confined to Eastern Hemisphere ... g 
Africa, Asia, Australia .*. 3 
Africa, Asia .. 2 
Confined to South-eastern Asia .... * * * * 4 
Total species probably introduced by water-birds . 
The second kind of species that may be introduced by becoming 
attached externally to birds is somewhat more difficult to deal with. 
Urena lohata, which is here clearly not a weed, may have been introduced 
in this way: its fruits sticking, burr-like, to the feathers of some bird; 
Buettneria andamanensis, might also have been thus introduced, thouo-h 
this is not so probable as in the other case. Three of the Desmodia— 
Desmodium triquetrum, D. laxifiorum and D. poly carp on—maj very well 
o we their introduction to this mode of dispersal. Boerhaavia repens, as has 
already been said, is probably sea-introduced, though there is no ’reason 
why it may not partly owe its dispersal to bird-agency. Its habitat 
on these islands is always the rocky headlands or isolated rocks along 
the coast on which sea-birds sit to devour the Grapsus crabs they capture 
on the wave-washed ledges below, and nothing is more likely than that 
the fruits may become at times attached to their feet and be carried at 
least from point to point along the coast. The Pisonias may both very well 
have been introduced in this fashion, though it is less likely as regards 
P, aculeata than as regards P. excelsa. From what has been already 
said of this tree in discussing it among the “ littoral ” species, it will 
be evident that its fruits are of such a nature as to admit of their being 
carried for great distances attached to a bird’s feet or body, if only the 
bird should happen to come in contact with them, and the objection that 
scraping-birds, which might do so, are not often migratory, while fruo-ivor- 
ous birds, which are migratory, would not come in contact with the Lmits 
because they are not likely to alight on a Pisonia, is not a valid 
203 
one. 
