Chapter Shandygaff to Shells of S by Brewer's Phrase & Fable

Shell (A) is a hollow iron ball, with a fuze-hole in it to receive a fuze, which is a plug of wood containing gunpowder. It is constructed to burn slowly, and, on firing, the piece ignites, and continues to burn during its flight till it falls on the object at which it is directed, when it bursts, scattering its fragments in all directions.

Shell Jacket (A). An undress military jacket.

Shell of an Egg After an egg in the shell has been eaten, many persons break or crush the empty shell. Sir Thomas Brown says this was done originally, “to prevent house-spirits from using the shell for their mischievous pranks.” (Book v., chap. xxiii.)

Shells on churches, tombstones, and used by pilgrims:
   (1) If dedicated to James the Greater, the scallop- shell is his recognised emblem. (See James.) If not, the allusion is to the vocation of the apostles generally, who were fishermen, and Christ said He would make them “fishers of men.”
   (2) On tombstones, the allusion is to the earthly body left behind, which is the mere shell of the immortal soul.
   (3) Carried by pilgrims, the allusion may possibly be to James the Greater, the patron saint of pilgrims, but more likely it originally arose as a convenient drinking-cup, and hence the pilgrims of Japan carry scallop shells.