10 
or membranaceous substance ; and that they resembled bone, in their 
hardening matter being secreted and deposited upon the membrana- 
ceous substance. It appeared that the gluten, in the porcellaneous 
shells, existed in so small a degree of natural inspissation, and was so 
little advanced in organization, that when the carbonate of lime was 
dissolved, even by very feeble acids, little or no vestige of jelly, mem- 
brane, or cartilage could be perceived. In the pearly shells, on the 
contrary, that substance, which served in the porcellaneous shells 
merely as a gluten, was not only more abundant, but also more inspis- 
sated, becoming visible and palpable. This chain of connexion 
between bone and shells, Mr. Hatchett found, was also extended 
between shells and corals. He found an exact similarity between the 
substances forming the various shells, and that which forms the various 
madrepores and millepores ; the nature of these bodies being so com- 
pletely the same, that the changes or gradations of the one are to be 
found in the other. Thus some madrepores and millepores, like the 
porcellaneous shells, afforded a gelatinous substance, on the removal 
of the carbonate of lime ; whilst others yielded a substance possessing 
all the characters of the membranaceous substance, contained in the 
shells formed of nacre or mother of pearl. 
Many of the circumstances which the expei’iments of Mr. Hatchett 
have made known, throw a considerable degree of light upon the for- 
mation of the different animal fossils, and will, therefore, be occasion- 
ally referred to in the succeeding pages of this work. 
