a8 Experiments and Ohfervat'ions 



was diiTolved; after which it remained in a perfectly coria- 

 ceous ftate, and complete in refpc6l to the original figure. 



The diflolved portion, being examined by the ufual prcci- 

 pitants, proved to be carbonate of lime, without any mixture 

 ofphofphate; but in another fpecies of the alterias, which 

 had twelve rays [ajlerias pappofa), I difcovered a fmall quan- 

 tity ofphofphate of lime. T am therefore induced to fufpcft 

 that, in the diflerent fpecies d the allcrias, nature makes an 

 imperfeft attempt to form fliell on fome, and a cruftaceous 

 coating on others; ; and that a feries of gradations is thus 

 formed between the teftaceous, the cruflaceous, and the 

 coriaceous marine animals. 



It was now requifite to afcertain if phofphate of lime is a 

 component part of the fubftance which covers the cruftaceous 

 marine or aquatic animals, fuch as the crab, lobftcr, prawn, 

 and crayfifh. 



Pieces of this fubftance, taken from various parts of thofe 

 animals, was at different times immerfed in acetous and in 

 diluted nitric acid; thofe which had been placed in the di- 

 luted nitric acid produced a moderate effervefcence, and in 

 a ftiort time were found to be foft and elaftic, of a yellovvifli- 

 white colour, and like a cartilage, which retained the original 

 figure. 



The fame effefts were produced by acetous acid, but in a 

 lefs degree ; in the latter cafe, alfo, a colouring matter re- 

 mained, and was folublc in alcohol. 



All the folutions, both acetous and nitric, afforded carbo- 

 nate and phofphate of lime, although the former was in the 

 largeft proportion. 



There is reafon to conclude, therefore, that phofphate of 

 lime, mingled with the carbonate, is a chemical charafteriftic 

 which diftinguiflies tlie cruflaceous from the teftaceous fub- 

 ftances; and that the principal difference in the qualities of 

 each, when complete, is caufed by the proportion of the har- 

 dening fiibftances relative to the gluten by which they are 

 cemented, or by the abundance and confiftcncy of the gela- 

 tinous, membranaceous, or cartilaginous fubftance, in and 

 on which the carbonate of lime, or the mixture of carbonate 

 and phofphate of lime, has been fecreted and depofited. 



Moreover, 



