14 ORGANS OF SUPPORT, 



particles of organized skeletons are removed, and have new 

 particles exuded in their place. There are some skeletons 

 of this class which retain an intermediate degree of conso- 

 lidation between the solid lithophytes and the horny flexible 

 keratophytes, as we see in theflustra and calcareous cetlaria, 

 where the proportion of earthy matter is very small com- 

 pared with the quantity of tough glutinous substance in their 

 flexible skeletons, and we observe them to be thin, soft, 

 transparent, and gelatinous all around their free and growing 

 margins. When these skeletons, whether horny or calcareous, 

 have once been consolidated, they are, like the shells of 

 articulata and mollusca, or like the antlers of the deer, no 

 longer susceptible of growth, and they enlarge or extend by 

 the successive additions of new matter, or of new parts. 

 The carbonate of lime is the common consolidating earth of 

 zoophytes, as silica is that of poriphera ; and these are two 

 of the most abundant materials of the mineral kingdom. 

 By the abundance of these calcareous lithophytes on the 

 shallow shores of the tropical seas, they prepare a rich soil 

 for new islands and continents to be raised by volcanic action 

 from the deep, while they at the same time tend to purify 

 the mass of the ocean for the maintenance of higher animals 

 by thus precipitating, in an insoluble state, the corrosive 

 materials conveyed incessantly into its bed by rivers that 

 wash the surface of continents. The deep purple colours of 

 the corrallium, the tubipora, the corallina, and many others, 

 the azure blue of the pocillopora, the bright yellow of the 

 melitaa, and all the other lively colours seen in these calca- 

 reous skeletons are removed by the action of heat, and do 

 not appear to depend on any peculiar mineral ingredient ; 

 and we observe the same animal nature of the colouring 

 matter in the shells of articulata and mollusca, and in the 

 coloured bones of many vertebrated animals. 



These skeletons of zoophytes are not exudations from the 

 surface of polypi ; the cell always precedes the existence of 

 the polypus which is developed within it. They are de- 

 veloped from the gelatinous substance of the reproductive 

 gemmules before any polypi begin to be formed, and they 

 continue to be developed and extended by the fleshy mass 

 of the zoophyte whether polypi are developed in the cells 

 or not. There is but one life, and one plan of development 



