SHELL, in natural history, a hard, and as it were stony covering, with which certain animals are defended, and thence called shell-fish.
As to the formation of a shell, it is now generally allowed to be formed by a viscous fluid composed of glue, and several sandy particles of an exquisite fineness, which are transmitted through an infinite number of little channels to the pores where it transpires, condenses, and hardens. When the animal increases in bulk, and the extremity of her body is not sufficiently covered, it continues to evacuate and build in the same manner, finishing or repairing her habitation. This viscous matter is proved, by undeniable experiments, to arise from the body of animals, and not from the shell, as some have imagined.