GROWTH OF ZOOPHYTES. 95 
Coral zoophytes 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. But Serpulas, 
and certain species of barnacles constituting the genus Criseis, fix 
themselves upon the living Astrea, Millepora, and other corals, and 
finally become imbedded by the increase of the zoophyte, without pro- 
ducing any defacement of the surface, or affecting its growth. Many 
of these Serpulas grow with the same rapidity as the zoophyte, and 
finally produce a long tube, which penetrates deep within the coral 
mass; and, when alive, they expand a large and brilliant circle or 
spiral of delicate rays, making a gorgeous display among the coral 
polyps. Instinct seems to guide these animals in selecting those corals 
which correspond with themselves in rate of growth; and there is in 
general a resemblance between the markings of a Criseis and the cha- 
racter of the radiations of the Astrea it inhabits. 
The effects of sediment on growing zoophytes are strongly marked, 
and may be often perceived when a mingling of fresh water alone 
produces little influence. We have mentioned that the Porites are 
reduced to flattened masses by the lodgment of sediment. ‘The same 
takes place with the hemispheres of Astree; 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 
Fungie, 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. Wherever streams or currents are moving or transport- 
ing sediment, there no corals grow; and for the same reason we find 
no living zoophytes upon sandy or muddy shores. 
The influence of temperature on the development of animal life, and 
the distribution of species is well known. But in no department is it 
more strikingly displayed than in that of zoophytes. In a former 
Report we have considered the general influence of temperature on 
the several divisions of this order of animals. The remarks which 
follow are consequently confined to the reef-forming species. We 
reserve for still another page the influence of this cause on the distri- 
bution of reefs, since we are occupied here with zoophytes as animal 
species, and not with reefs, a result from the growth of corals. 
The temperature of the ocean in which reef-corals grow is evidently 
the temperature congenial tothem. From a general survey of facts, it 
appears that these species are not met with where the winter tempera- 
ture remains much time below 66° I.; though a temporary reduction to 
64°, or even lower (as at the Bermudas), may occur. Where the tempe- 
