THE ARGONAUT. 



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ARGONAUT AS IT SWIMS BACKWARD (NATURAL 

 POSITION). 



and like many other molluscs, it can rise to the surface ; but there the arms are never employed 

 as oars : and those which have the broad expanded membranous disc are never used as 

 sails. Their true function, as ascertained by M. Rang, and confirmed by the experiments of Madame 

 Power, is the secretion of the substance of the shell. They are stretched tensely over its surface, and, 

 when accidental injuries arise, they deposit for its repair the needful quantity of shelly matter. To do 

 this, and to supply what is wanted for the enlargement 

 of the shell with the growth of the animal, is their 

 appointed duty, precisely similar to that of the mantle 

 in Sea Snails and bivalve shells. 



We have spoken of the shell of the Ai-gonaut as 

 an " external shell," but this is true so far only as regards 

 the fact (unique in the molluscan class) that the animal 

 is not actually attached, organically, in any way to its 



shell. But the shell itself is so completely enveloped and held fast by the expanded lobes 

 of the dorsal shell-secreting arms, that it may, without incoirectness, be called an "internal 

 shell," its delicate, almost paper-like substance, proving its entire unfitness for a protective covering 

 if exposed to the action of the sea. 



As before remarked, the female Argonaut alone secretes a shell, which serves as the cradle or 

 receptacle for the attachment of her eggs. The male, which is very much smaller than the female, 



is naked, and looks like a little Octopus with short, pointed arms. 

 The third arm, on the left side in the male, is specially modified, 

 and is said to be " hectocotylised," being in some instances entirely 

 detached, thus forming, as it were, a distinct organism, with independent 

 locomotory powers of its own. The " hectocotylus " of the Argonaut 

 resembles a little worm, with two rows of suckers along its length, 

 a long filiform appendage at one extremity, and a small swelling at 

 the other. When first discovered it was regarded as a parasite, and 

 termed Triclioceplialus acetabularis by Delle Chiaje, while the 

 corresponding body, found in an Octopus, was called Hectocotylus 



octopodis by Cuvier. At first it has the form of a sac, within which the slender terminal part of 

 the arm is coiled up. The sac then splits to give exit to the hectocotylus, and its two halves reunite 

 on the outer face of the base of the arm, forming a chamber for the reception of the spermatophores. 

 These are either placed within the mantle-cavity or fixed to the internal surface of the buccal 

 cavity of the female. The hectocotylus is in fact only an arm irregularly metamorphosed and 

 spontaneously detached. 



Four species of Argonaut are known ; these all inhabit the open sea, and have been 

 met with throughout the warmer parts of the globe. Captain King records the capture of a 

 Dolphin six hundred leagues from any land, from the stomach of which several Argonauts were 

 taken. 



The delicate paper-like shell of one species of Argonaut (the A. hians) has actually been met 

 with in a fossil state in the Tertiary deposits of Piedmont. The same species is now found living in 

 the China seas. 



FAMILY II. OCTOPODID^E. 



The members of this family have only an internal rudimentary, uncalcified shell, represented by 

 two short styles or plates, enclosed in the substance of the mantle. The arms are alike, but unequal 

 in length, and are united at their base by a broad web. They have two rows of suckers. The body 

 is oval in form and covered with wart-like prominences. 



The Common Octopus, found on the British shores (and now so familiar to us by the energetic 

 exertions of Mr. Henry Lee, F.L.S., and the managers of the Brighton Aquarium) is, perhaps, the 

 strangest of all the Cephalopodous class. Its bizarre figure and bright staring eyes, which never close, 

 cannot fail to excite astonishment when seen for the first time, especially when employed in the act 

 of walking on the floor of an aquarium, or in that of swimming by contraction of the membrane 



PAPER NAUTILUS IX ITS SHELL. 



