VOL. LXXXIX.] PHILOSOPHICAL TRANSACTIONS. 557 



not acquainted with any experiments by which the chemical nature of the substance 

 which covers crustaceous marine animals had been determined, I was desirous to 

 ascertain in what respect it was different from shell, and I began these experiments 

 on 3 species of the echinus, with which I had been favoured by the Right Hon. 

 President. I was the more inclined to begin with the echini, because naturalists 

 do not appear to be perfectly agreed, whether to call them testaceous or crustaceous 

 animals. Klein, who has written a work on echini, after having noticed the various 

 opinions of Rondelet, Rumphius, and others, determines that they are to be re- 

 garded as testaceous animals. But Linnaeus was of the contrary opinion, as appears 

 from his definition of the echinus. " Corpus subrotundum, crusta ossea tectum, 

 spinis mobilibus saepius asperum." 



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

 animals were composed of carbonate of lime, without any phosphate, I thought it 

 very possible, that the covering of the crustaceous animals might, in some respect, 

 be different, and if so, I should thus, by chemical characters, be enabled to ascer- 

 tain the class to which the echinus was to be referred. Of the 3 echini which were 

 examined, one had small spines; the 2d had large obtuse spines; and the 3d was of 

 a very flat form. Portions of these echini were separately immersed in acetous, 

 muriatic, and diluted nitric acid, by each of which they were completely dissolved, 

 with much effervescence ; depositing, at the same time, a thin outer skin or epi- 

 dermis. The transparency of the solutions was also disturbed by a portion of gluten, 

 which remained suspended, and communicated a brownish colour to the liquors. 

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

 acetous solution of each echinus, I obtained a precipitate of phosphate of lead, by 

 the addition of acetite of lead ; and, having thus proved the presence of phosphoric 

 acid, I saturated the nitric solutions with pure ammonia, by which a quantity of 

 phosphate of lime was obtained, much inferior however in quantity, to the carbonate 

 of lime, which was afterwards precipitated by carbonate of ammonia. The com- 

 position of the crust of the echinus is therefore different from that of marine shells ; 

 and, by the relative proportions and nature of the ingredients, it approaches most 

 nearly to the shells of the eggs of birds ; which, in like manner, consist of car- 

 bonate, with a small proportion of phosphate of lime, cemented by gluten. 



It remained now to examine the composition of those substances which are de- 

 cidedly called crustaceous ; but previous to this, some experiments were made on 

 the asterias or star-fish, of which I took the species commonly found on our coasts, 

 and known by the popular name of five fingers, asterias rubens. The asterias is 

 thus described by Linnaeus. " Corpus depressum, subtus sulcatum: crusta coriacea, 

 tentaculis muricata." When the asterias was immersed in the acids, a considerable 

 effervescence was produced, and a thin external stratum was dissolved ; after which 

 it remained in a perfectly coriaceous state, and complete, in respect to the original 

 figure. The dissolved portion, being examined by the usual precipitants, proved 

 to be carbonate of lime, without any mixture of phosphate ; but in another species 



