Growth, and Habits of Coral Zoopht/tes. 53 



nacles, constituting the genus Criseis, fix themselves upon 

 the living Astrsea, Millepora, and other corals, and finally 

 become imbedded by the increase of the zoophyte, without 

 producing any defacement of the surface, or affecting its 

 growth. Many of the Serpulas grow with the same rapidity 

 as the zoophyte, and finally produce a long tube, which pe- 

 netrates 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 character of the radiations of the Astraea it in- 

 habits. 



The efi^ects 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 men- 

 tioned that the Porites are reduced to flattened masses by 

 the lodgment of sediment. The same takes place with the 

 hemispheres of Astrsea ; and it is not uncommon that in this 

 way large areas at top are deprived of life. The other por- 

 tions still live unaff'ected by the injury thus sustained. Even 

 the Fungise, which are broad simple species, are occasionally 

 destroyed over a part of the disk through the same cause, 

 and yet the rest remains alive. Wherever streams or cur- 

 rents are moving or transporting 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 gene- 

 ral influence of temperature on the several divisions of this 

 order of animals. The remarks which follow are conse- 

 quently confined to the reef-forming species. We reserve 

 for still another page the influence of this cause on the dis- 

 tribution 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 



