40 James D. Dana, Esq., on the Structure^ 



secretions, belongs almost exclusively to coral polyps. This 

 is reproduction by buds, and the process is so similar to the 

 production 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 instances thousands, or hundreds of thou- 

 sands, have proceeded from a single one, and the colony has 

 spread to a large size. Such is the Madrepora and Astroea. 

 There are modifications of this process 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 

 compound 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 numerous mouths and 

 as many stomachs. In some species the coalescence is con- 

 fined to the lower half of the polyps, or to a still less part ; 

 and in this case the animals project above the general liv- 

 ing 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 

 appearance true actiniae. The existence of coral in the living 

 coral zoophyte is nowhere apparent, and would not be sus- 

 pected 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 



