ARGONAUT. 349 



imagined to have been really formed by an animal allied to that 

 genus. It has been proved, however, by the interesting ex- 

 periments of Madame Power (who has kept a number of these 

 animals in a kind of cage inclosed from the sea in the bay of 

 Messina), that the shell increases regularly with the growth of 

 the animal ; and that the Mollusk possesses the power of repair- 

 ing the shell when injured, in a manner corresponding to its 

 original formation ; whence no reasonable doubt can exist, that 

 the Argonaut is the real constructor of it. 



963. Of the eight arms of the Argonaut, six taper gradually 

 towards the extremities ; but two are expanded into wide mem- 

 branous flaps. From very early times, this animal has been 

 reputed to swim on the surface of the sea, using its arms as oars, 

 and spreading these expanded membranes as sails, so as to be 

 wafted along by the wind. But it is now known by accurate 

 observation of the living animal, that this is altogether a fiction 

 (though an interesting one) ; and that the expanded membranes 

 are spread over the sides of the shell, meeting along its keel or 

 edge, and completely inclosing it. It is by these, indeed, and 

 not by the surface of the body itself, that the calcareous secre- 

 tion is poured out, for the enlargement or reparation of the shell. 

 It will be observed that there is a double row of suckers along 

 the edge of each of the expanded arms ; and by these suckers 

 they are held in close contact with each other along the keel of 

 the shell. When the animal withdraws its whole body into the 

 shell, the exterior of the latter is about half uncovered, the ex- 

 panded arms also being partly drawn in. By the action of the 

 arms, and the expulsion of water from its branchial chamber, the 

 Argonaut can swim backwards in the same manner as other 

 Octopods ; and it can also creep along the bottom of the sea. 



964. The Decapod section, which, besides the eight ordinary 

 arms, has two longer and slenderer ones, usually denominated 

 tentacles, presents many points of approach to the Tetrabranchi- 

 ate Order. This affinity is indicated, not merely by the in- 

 creased number of the external arms, but by their smaller size 

 in proportion to the body, by the frequent development of a 

 second row of small tentacula within the others, and by several 



