360 THE WEBBED SEPIA. 



slightest possible resistance to the water through which it passes, keeps its velated arms 

 stretched tightly over the shell, and then, by violently ejecting water from the siphon, 

 drives itself, by the reaction, in the opposite direction. 



The uppermost figure in the illustration shows the Argonaut in the act of swimming. 

 The extremity of the siphon is seen projecting immediately below the eye, and the reader 

 will at once understand that if the action forcibly ejects water from the tube, the effect 

 will be to drive the unimal rapidly in the contrary direction, i.e. from right to left, as seen 

 in the engraving. The third figure represents an empty shell, and is given for the purpose 

 of showing the partially spiral and deeply grooved keel, as well as the extreme tenuity 

 of the shell itself. 



The animal, or poulp, is very slightly connected with the shell, and, when captured in 

 a net, will sometimes voluntarily leave its home. Many persons have therefore thought 

 that the poulp was not the fabricator of the shell, but only an intruder on the premises 

 of the rightful owner, having taken possession of the shell as a defence for its soft body, 

 just as the well-known soldier or hermit crab arms its soft and unprotected tail with the 

 shell of a whelk, periwinkle, or a trochus. This opinion, ingenious and deserving of 

 examination as it was, has, however, been proved erroneous by a number of experiments, 

 which have shown that the Argonaut is not only the occupier, but the architect of its 

 graceful dwelling, and that the expanded arms are at once the 'furnishers of the material 

 and the executors of the work. 



The precise food of the Argonaut is not ascertained, but Mr. Bennett presumes that, 

 as he always found the globular and translucent, but empty shells of the hyalea, one of 

 the wing-footed marine species, adhering in numbers to the discs on the Argonaut's arms, 

 these creatures must have been captured and devoured b^y the more powerful mollusc. 



As the various cephalopods are so numerous as to preclude all possibility of figuring 

 and describing each species, we must therefore content ourselves with a typical form of 

 each family, and a general account of its members. 



The species belonging to the family of the Octopodidse, or Eight-armed Cuttles, 

 possess no external shell like that of the nautilus, its place being taken by two short 

 styles or " pens " in the substance of the mantle. There are eight arms, unequal in 

 length, and furnished with double or single rows of the suckers which have already 

 been described. 



They are solitary beings, voracious to a degree, and so active that they find little 

 difficulty in capturing their prey, or in escaping from the attacks of their enemies. Even 

 when pursued into the narrow precincts of a rock pool, the creature is not easily caught. 

 When threatened, or if apprehensive of danger, the Polypus, as the animal was formerly 

 called, darts with arrowy swiftness from one side of the pool to the other, and at the 

 same time so discolours the water with the contents of its ink-bag, that its course is not 

 perceptible, nor, until the water has become clear again, can the precise locality of the 

 creature be discovered. Even if detected, it is not easily captured, as it has a knack of 

 forcing its unprotected body into some crevice, so that no hold can be taken of it, and 

 then affixing itself by its suckers to the rock with such wonderful tenacity that it can 

 hardly be detached as long as life remains. 



One example of this family is the WEBBED SEPIA, a very curious animal, found on 

 the coast of Greenland. Its colour is violet, and the arms are united by a web almost to 

 their tips. The suckers are set in single rows. Only one species of this genus is known. 



In the Octopods the suckers are set directly upon the arms, and the eyes are fixed in 

 their orbits ; but in the Decapods, another section of these creatures, the suckers are 

 placed on footstalks, and armed with a bony ring on each. The eyes are movable, and 

 the shell is internal, lying loosely in the mantle. This so-called shell has, however, no 

 real title to the name, being either a spear-shaped body of a horny substance, such as 

 is popularly known by the name of sea-pen, or a curious aggregation of chalky particles, 

 familiar under the title of "cuttle-bone." This "bone" is not attached to the animal by 

 any muscles, but lies loosely in a kind of sac in the mantle, and will drop out if the sac 

 be opened. 



