"Light as a flake of foam upon the wind,
Keel upward from the deep, emerged a shell.
Shaped like the moon ere half her horn is fill'd ;
Fraught with young life, it righted as it rose,
And moved at will along the yielding water.
The native pilot of this little bark
Put out a tier of oars on either side,
Spread to the wafting breeze a twofold sail,
And mounted up, and glided down the billow,
In happy freedom, pleased to feel the air,
And wander in the luxury of light." — Pelican Island.
The accuracy of modern research, however, has proved this to be but a pleasant fable. The Argonaut is a Cuttle-fish, and crawls along the bottom, like its fellows, by means of its slender, flexible, tentacular arms, as represented in the preceding engraving, (fig. 2); while the pair that are furnished with a broad fleshy disk, have an office very different from that of sails, namely, that of forming, repairing, and protecting the thin and papery shell. (See fig. 3.) Its only swimming power appears to be that which it possesses in common with all Cephalopoda, of shooting along in a backward direction, by the force of a jet of water from the funnel, as shown at fig. 1, where it is represented as swimming towards the point a.
Among the Tunicata there are some singular tribes which swim freely in the sea. "The Salpœ, translucent as their native waters, and often united in chains, after a pattern peculiar to each species, are driven along the surface with considerable quickness by alternate contractions and expansions, and by the propulsion they receive from a current of water, which is made continually to traverse the long diameter of the body, sucked in by the posterior aperture, and issuing in a stream through that on the side of the mouth. Hence the body is
