20 
ATOLLS. 
Ch. I. 
other and unexpected agents at work here : large shoals 
of two species of Scams, one inhabiting the surf outside 
the reef and the other the lagoon, subsist entirely, as I 
was assured by Mr. Liesk, the intelligent resident before 
referred to, by browsing on the living polypifers. I 
opened several of these fish, which are very numerous 
and of considerable size, and I found their intestines 
distended by small pieces of coral, and finely ground cal- 
careous matter. This must daily pass from them as the 
finest sediment ; much also must be produced by the 
infinitely numerous vermiform and molluscous animals 
which make cavities in almost every block of coral. Dr. 
J. Allan of Forres, who has enjoyed the best means of 
observation, informs me in a letter, that the Holuthurise 
(a family of Eadiata), subsist on living coral ; 1 and the 
singular structure of bone within the anterior extremity 
of their bodies, certainly appears well adapted for this 
purpose. The number of the species of Holuthuria, 
and of the individuals which swarm on every part of 
these coral-reefs, is extraordinarily great ; and many 
ship-loads are, as is well known, annually freighted 
for China with trepang, which is a species of this 
genus. The amount of coral yearly consumed, and 
ground down into the finest mud, by these several crea- 
tures, and probably by many other kinds, must be 
immense. These facts are, however, of more importance 
1 [Mr. Guppy, Proc. E. S. Edin. xiii. p. 894, expresses the opinion 
that the Holothurians do not subsist on the living coral, but obtain 
nutriment from swallowing the sand and detrital material, of which 
broken coral forms a large constituent.] 
