50 ON CORAL REEFS AND ISLANDS. 



One of the most singular peculiarities of polyps is their ready 

 restoration of a lost part. Even a fragment will go on to com- 

 plete the entire animal again : as with the fabled hydra of old, 

 the knife is used but to multiply, for every section becomes a 

 new animal. 



In all the points mentioned in the description here given, the 

 polyp of ordinary coral and the actinia are identical. 



b. Process of Budding. — There is one mode of reproduction 

 which, although having no necessary connection with coral se- 

 cretions, belongs almost exclusively to coral polyps. This is re- 

 production by buds ; and the process is so similar to the produc- 

 tion of buds in vegetation, that a remembrance of the latter will 

 aid much in conceiving of it. The bud generally commences 

 as a slight prominence on the side of the parent : the prominence 

 enlarges, and soon a circle of tentacles grows out, with a mouth 

 at the centre ; enlargement goes on till the young finally equals 

 the parent in size. Thus by budding, a compound group is 

 commenced ; and it is evident that if the parent and the new 

 polyp go on budding again, and so on, the compound group may 

 continue to enlarge. This is the fact in nature. The polyps, 

 one and all, continue propagating by buds, until in some instan- 

 ces thousands, or hundreds of thousands, have proceeded from a 

 single one, and the colony has spread to a large size. Such is 

 the Madrepora and Astrsea. There are modifications of this pro- 

 cess, analogous to those in vegetation, but we need not dwell 

 upon them in this place. 



It is obvious that the connection of the polyps in such a com- 

 pound group must be of the most intimate kind. The several 

 polyps have separate mouths and tentacles, and separate stomachs ; 

 but beyond this there is no individual property. They coalesce, 

 or are one, by intervening tissues, and there is a free circulation 

 of fluids through the many pores or lacunes. The zoophyte is 

 like a living sheet of animal matter, fed and nourished by nu- 

 merous mouths and as many stomachs.- [n some species the 

 coalescence is confined to the lower half of the polyps, or to a 

 still less part ; and in this case the animals project above the gen- 

 eral living surface. Polyps thus clustered, spreading at summit 

 a star of tentacles, constitute the flowering zoophytes of coral 

 reefs. 



Those coral animals which do not bud are to all external ap- 

 pearance true actiniae. The existence of coral in the living coral 

 zoophyte is nowhere apparent, and would not be suspected if not 

 previously known ; for, as before stated, it is wholly internal, 

 and the visible exterior is the fleshy skin of the polyp. 



c. Secretion of Coral. — We have already remarked on the gen- 

 eral nature of coral secretions. These secretions, it should be 

 farther observed, increase within simultaneously with growth, 



