DESCRIPTION OF THE EXPEDITION. 53 
could hide, and partly the fact that the strong growth of sedentary organisms by cover- 
ing over the rock with organic substance prevented the entrance into it of destructive 
organisms, such as boring algze, sponges, worms, and molluscs, on the products of which 
so many free-living animals—burrowers, sand-feeders, and scavengers—thrive. The chief 
coral was a green Stylophora, which quite took the place of the Wadrepora and Porites 
of other atoll-lagoons. Its relatively blunt, massive branches were mostly thickened at 
their ends with the galls of a crab, Hapalocarcinus. A colony of Madrepora or branch- 
ing Porites usually yields a rich variety of crustaceans, starfishes, molluscs, and other 
animals when broken up, but this coral was scarcely infested by a single form beyond 
the delicate Melia tessellata. This little crab, so conspicuous in its purple and orange 
body, carries a small green palythoid anemone in each of its slender chele, making use 
of their thread-cells probably both for protection and for securing prey. 
Land on an exposed reef is always to a certain degree in a condition of change. Sand 
is piled up at one end of an island while one wind prevails, only to be washed away and 
carried to the other end when it blows from the opposite quarter. The six islands now 
existing are probably merely the remains of an island once continuous along the whole 
southern side. A junction by a sand-barrier of the lagoon half of Ile des Rats to fle 
Sipaille has been a recent change, while the outer half of the former has been made into 
a separate island. 
The islands themselves are very like those of Salomon, with similarly situated areas of 
coral-rock, sand, and sand-rock (or tuffe). All have a tendency to be slightly hollowed 
out and marshy in their centres, though their surfaces in most places lie well above the 
high-tide level. In the centre of Lubine we found one such marsh covered with reeds 
8 feet in height, a condition not found elsewhere on any coral-islands we have visited 
in the Indian Ocean (PI. 10). It was like a Mauritian or Ceylon swamp, and presented a 
most refreshing feature to the eye. It is unlikely that its reed was intentionally intro- 
duced, as it is not used for house-thatching or any other purpose. In most places the 
soil is relatively abundant and richly impregnated with phosphate of lime from former 
bird-colonies. Ile Sudest has a large grove in its centre of badamier (Terminalia 
Catappa), valuable for its almond-like nuts, while everywhere the growth of ferns and 
herbaceous plants is extraordinarily rich. The jungle-trees were the same as elsewhere, 
but there was no trace of the former existence of any gayac. Mangroves were absent, 
though there were many places along the shore eminently suitable for their growth. 
Indeed, they were not seen throughout the whole Chagos, a singular fact when we 
consider their extraordinary adaptability to marine transport. 
As elsewhere, we devoted great attention to the land-fauna, but found it very scanty 
and difficult to collect. Rats and mynahs (the Indian starling) had been introduced, 
the latter intentionally, so that almost only those insects which hide themselves away 
have managed to survive. Geckos are exceedingly scarce and mosquitoes consequently 
are a plague everywhere. However, we found our first land-shell in the decaying trunk 
of a “ bois blanc” (Hernandia), and some beetles, which ordinarily live in guano. Birgus 
is common—lle Sipaille is called after it—and does enormous damage. Together with 
the rats it is responsible for the destruction of as much as a third of the coconut-crops, 
