The name applied to both shows that each has long been compared to a ship, as you may see more fully in Webster's Dictionary, or the "Encyclopedia," to which he refers.

If you will look into Roget's Bridgewater Treatise, you will find a figure of one of these shells, and a section of it.
The last will show you the series of enlarging compartments successively dwelt in by the animal that inhabits the shell, which is built in a widening spiral.

Can you find no lesson in this?
THE CHAMBERED NAUTILUS.
This is the ship of pearl, which, poets feign, Sails the unshadowed main,-- The venturous bark that flings On the sweet summer wind its purpled wings In gulfs enchanted, where the siren sings, And coral reefs lie bare, Where the cold sea-maids rise to sun their streaming hair Its webs of living gauze no more unfurl; Wrecked is the ship of pearl! And every clambered cell, Where its dim dreaming life was wont to dwell, As the frail tenant shaped his growing shell, Before thee lies revealed,-- Its irised ceiling rent, its sunless crypt unsealed! Year after year beheld the silent toil That spread his lustrous coil; Still, as the spiral grew, He left the past year's dwelling for the new, Stole with soft step its shining archway through, Built up its idle door, Stretched in his last-found home, and knew the old no more.
Thanks for the heavenly message brought by thee, Child of the wandering sea, Cast from her lap forlorn! From thy dead lips a clearer note is born Than ever Triton blew from wreathed horn! While on mine ear it rings, Through the deep caves of thought I hear a voice that sings:- Build thee more stately mansions, O my soul, As the swift seasons roll! Leave thy low-vaulted past! Let each new temple, nobler than the last, Shut thee from heaven with a dome more vast, Till thou at length art free, Leaving thine outgrown shell by life's unresting sea!.