CAUSHS AFFECTING THE GROWTH OF CURALS. by | 
ment of sediment. The same takes place with the hemispheres 
of Astrea; and it is not uncommon that in this way large 
areas at top are deprived of life. The other portions still live 
unaffected by the injury thus sustained. Even the Fungia, 
which are broad simple species, are occasionally destroyed over 
a part of the disk through the same cause, and yet the rest re- 
mains alive. It is natural, therefore, that wherever streams or 
currents are moving or transporting sediment, there no corals 
grow ; and for the same reason we find few living zodphytes 
upon sandy or muddy shores. 
The small lagoons, when shut out from the influx of the 
sea, are often rendered too salt for growing zodphytes, in con- 
sequence of evaporation,—a condition of the lagoon of Ender- 
by’s Island. 
They also are liable to become highly heated by the sun, 
which likewise would lead to their depopulation. 
Coral zodphytes sometimes suffer injury from being near 
large fleshy Alcyonia, whose crowded drooping branches lying 
over against them, destroy the polyps and mar the growing 
mass. Again, the dead parts of a zodphyte, though in very many 
cases protected by incrusting nullipores, shells, bryozoans, etc., 
as already explained, in others is weakened by boring shells 
and sponges. Agassiz states, in his paper on the Florida 
Reefs (Coast Survey Report for 1851): ‘‘ Innumerable bor- 
ing animals establish themselves in the lifeless stem, piercing 
holes in all directions into its interior, like so many augurs, 
dissolving its solid connection with the ground, and even pen- 
etrating far into the living portion of these compact communi- 
ties. The number of these |horing animals is quite incredible, 
and they belong to different families of the animal kingdom ; 
among the most active and powerful we would mention the 
date-fish or Lithodomus, several Saxicave, Petricole, Arce, 
