MOLLUSCA. 93 



is derived. The body is obtuse posteriorly, with fins (fin-like expansions), 

 and the interior dorsal shell is wanting. As the name implies, it has eight 

 arms. The species figured attains a length of two feet and a half, including 

 the arms, which constitute considerably the longest portion. It creeps upon 

 the oround with the mouth downwards, drawing itself along by means of 

 the circle of arms ; or leaving the bottom, it swims backwards by flapping 

 the fleshy disk from which the arms arise. It is provided with an ink bag. 

 The eyes can be covered with the surrounding skin, in the manner of an 

 eyelid. There are two complicated branchiae somewhat like a fern leaf, 

 through which the blood is forced, by a heart at the base of each; a third 

 heart, near the bottom of the cavity, receives the oxygenated blood, and dis- 

 tributes it through the body. It is eaten on the shores of the Mediterranean. 

 Argonauta {A. argo^ JAim., pi. 76, fig. 17), six or seven inches long, has 

 a closely rolled involuted shell without partitions, laterally compressed, 

 tuberculate, very thin, white, translucent, with the last turn including the 

 rest. This is the Nautilus of the ancient authors, who were acquainted 

 with A. argo., the Mediterranean species, about the sailing of whicli so many 

 fables have been related, as in the following lines from the '^ Pelican Island." 



" Light as a flake of foam upon the wind, 

 Keel upwards from the deep emerged a shell, 

 Shaped like the moon ere half her horn is filled; 

 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." 



For a long time naturalists considered the maker of the shell of Argonauta 

 to be unknown, believing the inhabitant found in it to be a parasite, like 

 the crabs which take possession of the empty shells of the spirivalve 

 mollusca; and they were led to this belief, by the fact that there is n(> 

 muscular attachment between the animal and the shell, presenting a 

 peculiarity which is unique among the mollusca. The animal has eight 

 arms, two of which have wide expansions at the extremity, which are 

 applied one to each side of the shell, which is in fact secreted by their 

 internal surface; and should it be intentionally broken, the damage is 

 repaired by the same organs in ten or twelve days, a proof that the shell 

 belongs to no other animal. It creeps upon the bottom with the shell 

 above, or shoots through the water backwards by means of the funnel, with 

 the narrow part of the shell in advance, and the arms extended like a 

 rudder. When it retires within the shell, the expansions of the clasping 

 arms are partly withdrawn, leaving a little of the anterior portion of the 

 shell uncovered ; consequently, they are never extended as sails, as many 

 fabulous accounts would lead us to believe. See the Mag. Kat. Hist., 1839, 

 pp. 421 and 521 ; 1840, pp. 8 and 57. 



297 



