and Observations on Shell and Bone. 323 
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 epidermis. 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 ammoniac, by which 
a quantity of phosphate of lime was obtained, much inferior, 
however, in quantity, to the carbonate of lime, which was after- 
wards precipitated by carbonate of ammoniac. 
The composition of the crust of the Echinus is therefore dif- 
ferent from that of marine shells ; and, by the relative propor- 
tions and nature of the ingredients, it approaches most nearly 
to the shells of the eggs of birds; which, in like manner, consist 
of carbonate, with a small proportion of phosphate of lime, 
cemented by gluten. 
It remained now, to examine the composition of those sub- 
stances which are decidedly 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 de- 
“ pressum, subtus sulcatum : crusta coriacea, tentaculis muri- 
“ cata.” * 
When the Asterias was immersed in the acids, a considerable 
* Systema Natura. Edit. Gmelin. p. 3160. 
