558 PHILOSOPHICAL TRANSACTIONS. [ANNO 17 QQ. 



of the asterias, which had 12 rays, asterias papposa, I discovered a small quantity 

 of phosphate of lime, I am therefore induced to suspect that, in the different 

 species of the asterias, nature makes an imperfect attempt to form shell on some 

 and a crustaceous coating on others; and that a series of gradations is thus formed 

 between the testaceous, the crustaceous, and the coriaceous marine animals. 



It was now requisite to ascertain if phosphate of lime is a component part of the 

 substance which covers the crustaceous marine or aquatic animals, such as the crab, 

 lobster, prawn, and crayfish. Pieces of this substance, taken from various parts 

 of those animals, was at different times immersed in acetous, and in diluted nitric 

 acid; those which had been placed in the diluted nitric acid, produced a moderate 

 effervescence, and in a short time were found to be soft and elastic, of a yellowish - 

 white colour, and like a cartilage which retained the original figure. The same 

 effects were produced by acetous acid, but in a less degree; in the latter case also 

 the colouring matter remained, and was soluble in alcohol. All the solutions, both 

 acetous and nitric, afforded carbonate and phosphate of lime, though the former 

 in the larger proportion. There is reason to conclude therefore, that phosphate of 

 lime, mingled with the carbonate, is a chemical characteristic which distinguishes 

 the crustaceous from the testaceous substances; and that the principal difference 

 in the qualities of each, when complete, is caused by the proportion of the hard- 

 ening substances, relative to the gluten, by which they are cemented; or by the 

 abundance and consistency of the gelatinous, membranaceous, or cartilaginous 

 substance, in and on which, the carbonate of lime, or the mixture of carbonate 

 and phosphate of lime, has been secreted and deposited. And, as the presence of 

 phosphate of lime, mingled with carbonate appears to be a chemical character of 

 crustaceous marine animals, there is every reason to conclude that Linnaeus did 

 right not to place the echini among the testaceous ones. 



The presence of phosphate of lime, in the substance which covers the crusta- 

 ceous marine animals, appears to denote an approximation to the nature of bone, 

 which, not only by the experiments of Mr. Gahn, but by the united testimony of 

 all chemists, has been proved principally to consist, as far as the ossifying substance 

 is concerned, of phosphate of lime. This consideration therefore induced me to 

 repeat the above experiments, on the bones of various animals. It is scarcely 

 necessary to mention the usual effects of acids on bones steeped in them, as they 

 are known to every physiologist and anatomist. In every operation of this nature, 

 the ossifying substance, which is principally phosphate of lime, is dissolved, and a 

 cartilage or membrane, of the figure of the original bone, remains; so that the 

 first origin of bones appears to be by the formation of a membrane or cartilage, of 

 the requisite figure, which, when the subsequent secretion of the ossifying sub- 

 stance takes place, is penetrated by it, and thus becomes more or less converted 

 into the state of bone. It is also known, that the nature of the bone is more 

 influenced by the greater or less predominance of the membranaceous or cartilagi- 

 nous part, than by any other cause. It is not therefore for me to add any thing to 



