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vertebrate animal do its bones ; an act wholly involuntary in both 

 cases. 



Therefore, when we speak of the labors or architecture of the coral 

 animal, we do not imply outside mechanical work as the bee in con- 

 structing its comb, but simply the operation of a vital function. " This 

 process of secretion," says Prof. Dana, " is one of the first and most 

 common of those that belong to living tissues. It belongs eminently 

 to the lowest kinds of life. These are the best stone-makers, for in their 

 simplicity of structure they may be almost all stone, and still carry on 

 the processes of nutrition and growth." 



The young polype in the reef-building species arises by a process of 

 budding from the parent animal. It was from this curious operation 

 that early observers strengthened their argument in favor of the vege- 

 table nature of corals. " The bud," says Dana, " commences as a slight 



Fig. 7. 



Brain -coral. 



prominence on the side of the parent. The prominence enlarges, a 

 mouth opens, a circle of tentacles grows out around it, and increase 

 continues until the young finally equals the parent in size. Since in 

 these species the young do not separate from the parent, this budding 

 produces a compound group." 



From this it is obvious that, while the polypes exist as individuals, 



