Why do not the crab and lobster appear "thin" when ill fed?

Because the stomach is formed on a bony apparatus, in short, a species of skeleton ; and does not therefore collapse when empty. Hence the policy of choosing crabs and lobsters by their weight.

Why is the food of the crab and lobster sure to be perfectly masticated?

Because to certain parts of the bony structure of the stomach, round its aperture communicating with the small intestines, (or the pylorus) the teeth are affixed. They are extremely hard, and serrated, or jagged, and as they surround the tube near the pylorus, nothing can pass that has not been duly prepared. These bones and teeth (the latter three in number) are moved by peculiar muscles, and in the craw-fish are known to be annually reproduced.

Why do some crabs attach, by a glutinous matter, the leaves of sea-weeds to their body?

Because they may thus completely conceal their form, and secure themselves from the detection of their enemies.

Why are the two calcareous concretions (commonly called crabs' eyes), found in summer at both sides of the stomach of the craw-fish?

Because they furnish the principal materials from which the new shell is hardened. Some are naturally red, whilst others remain black, even when boiled ; and some reach the age of twenty years.