504 Experimints and Ohfervalions on Shdl and Bone, 



any in the helix memoralu^ it may be doubted whether the prefence of phofphate of lime 

 fliQuld be confidered as a chemical -charadter of land fhells *. 



Experiments on the covering Suhjiance of Crujlaceous Marine Animals f . 



As I was not acquainted with any experiments, by which the chemical nature of the 

 fubftance which covers Cruftaceous marine animals had been determined, I was defirous to 

 afcertaln in what refpeft it was different frorn fliell ; and I began thefe experiments on 

 three fpecies of the echinus, with which I had been favoured by the Right Hon. Prefident. 

 I was the more inclined to begin with the echini, becaufe naturalifts do not appear to 

 be perfeftly agreed, whether to call them teftaceous or cruftaceous animals. 



Klein, who has written a work upon echini, after having noticed the various opinions 

 of Rondelet, Rumphius, and others, determines that they are to be regarded as teftaceous 

 animals. His words are, " Sic plurimas teftas marinas, in ftatu natural! confideratas, cum 

 " echinodermatis potius quam cum cruftis aftacorum vel cancrorum conferre licebit. 

 " Itaque echinoderma cum Ariftotele qui echinos inter teftacea quibus facultas ingredi- 

 " endi eft reponit, nee non cum Belonio, Aldrovando, et excellentiflima Sloanio religiofe 

 " teftam appcllamus, quam fatis duram in nonnullis offendimus J." 



But Linnaeus was of the contrary opinion, as appears from his definition of the echinus. 

 " Corpus fubrotundum crujla ojfea teElum fpinis mobilibus fjepius afpera §." 



Now as the experiments above related had proved, that the fhells of marine animak 

 were compofed of carbonate of lime, without any phofphate, I thought it very pollible 

 that theVovering of the cruftaceous animals might, in fome refpedl, be different; and if 

 fo;^ I fhould thus by chemical charadters, be enabled to afcertain the clafs to which th© 

 ccliinus was to be referred. 



Of the three echini which were examined, one had fmall fpines ; the fecond had large 

 obtufc fpires; and the third was of a very flat form. 



Portions of thefe echini were feparately immerfed in acetous, muriatic, and diluted 

 nitric acid, by each of which they were compleatly diflblved with much eflervefcence ; 

 depoGting at the fame time a thin outer ikin, or epidermis. The tranfparency of the fo- 

 lutions was alfo difturbed by a portion of gluten which remained fufpended, and commu- 

 nicated a brownlfli colour to the liquors. 



The folutlons in acetous and diluted nitric acid were filtrated ; after which, from the 

 acetous folution of each echinus, I obtained a precipitate of phofphate of lead, by the ad- 



• Some experiments which I have lately made upon the cuttle bone of the fliops have proved, that the 

 terra bone is here mifapplied; if the prefence of phofphate of lime is to be regarded as the charafleriftic of 

 bone 5 for this fuhftaiice in compofition is exaftly fimilar to (liell, and confifts of various membranes har- 

 dened by carbonate of lime, without the fmalleft mixture of phofphate. 



t Under this head I have included my experiments upon echini ftar-iifli, crabs, lobfters, &c. 



X Klein Naturatis diffofitia Echinodermatum, (Sc. p. ig, 



§ Syfiema Natura, Edit. Gmelin, p. 3168. 



dltion 



