91 



which in their most perfect condition are well defined and 

 distinct from each otlier, become confused, from having inter- 

 vening depressions filled up with calcareous matter, and the 

 interspaces or meshes on the surface disappear from the same 

 cause. In this way all the specific characters are destroyed ; 

 the surfaces become plain and even, and the apertures look 

 like minute orifices in a plain incrustation. The apertures, 

 like the surface, loose their specific distinctions and become 

 smaller, till by the continued deposit of calcnreous matter* 

 they become obliterated and the polypes thus beeome en- 

 closed in graves of their own making. This being the case, 

 a further effusion of pulp takes place on the surface of the 

 destroyed cells; in it new cells and polypes are developed, 

 to be again destroyed by the very process which gave them 

 life. Thus we see 



-The living pile ascend, 



The mausoleum of its architects, 



Still dying upwards as their labours closed." 



From these repeated obliterations it is, that many species 

 become so irregular in shape; a remarkable instance of which 

 is found in the common pumice stone coralline, ( Cellepora 

 pumiccsa.J 



We thus see that the external surface of the cells is per- 

 petually undergoing changes of a very marked character. Is 

 this consistent with an extravascular and inorganic character? 



If these calcareous cells, in reality have no organic cha- 

 racter, but are merely formed by, or are an exudation from 

 the pulp, or from a secreting membrane, it is evident, that 

 after their first formation they could undergo no alteration 

 either in form or character, except what would arise from a 

 chemical or mechanical change in their structures. The 

 external surface once formed, would remain for ever beyond 

 the influence of the polype within. If inorganic bodies be 

 surrounded by highly organized tissues, life is sometimes 

 sufficiently powerful to cause their removal. But in the case 

 under consideration, the lime is not moulded on the pulp, by 

 a mantle, as in shells; but is formed in and by the pulp 

 itself, and a continued deposition is going on. If the external 

 layer be beyond the influence of life, the lime ought to be 

 deposited on the internal surface as being most in contact 

 with the exuding pulp, and thus, the cavity of the cell 

 would beeome filled and solid, rather than the fissures of the 

 exterior. But the exact reverse of this is the case. In 

 some species, such as Calepora cervicornis, and ramulosa, 

 the Sea Mats ; Eschar a foliacea, and others, the whole pro- 

 cess of formation, from the embryo, to the perfect and 

 obliterated cells, can be observed ; so that no difficulty can 

 arise for want of opportunities to lest these opinions. In 



