520 Mr. Hatchett’s Experiments 
and the growth and age of the animal become denoted, by the 
number of the strata which concur to form the shell. 
Although the Haliotis Iris and the Turbo olearius are com- 
posed of the true mother of pearl, I was induced to repeat the 
foregoing experiments, on some detached pieces of mother of 
pearl, such as are brought from China. 
These experiments I need not describe, as the results were 
precisely the same. 
I must, however, observe, that the membranaceous or carti- 
laginous parts of these shells, as well as of the pieces of mother 
of pearl, retained the exact figure of the shell, or piece, which 
had been immersed in the acid menstruum ; and these membra- 
naceous parts distinctly appeared to be composed of fibres placed 
in a parallel direction, corresponding to the configuration of the 
shell. 
The same experiments were made on pearls; which proved 
to be similar in composition to the mother of pearl; and, so 
far as their size would enable me to discern, they appeared 
to be formed by concentric coats of membrane and carbonate 
of lime; by this structure, they much resemble the globular 
calcareous concretions, found at Carlsbad and other places, 
called Pisolithes. 
The wavy appearance and irridescency of mother of pearl, 
and of pearl, are evidently the effect of their lamellated struc- 
ture and semitransparency ; in which, in some degree, they are 
resembled by the lamellated stone called Adularia. 
When the experiments on the porcellaneous shells, and on 
those formed of mother of pearl are compared, it appears, that the 
porcellaneous shells are composed of carbonate of lime, cemented 
