3300 



THE MOLLUSKS OR SHELLFISH 



eluded that the shell was formed by another mollusk, and was merely taken posses- 

 sion of by the cephalopod, as a convenient abode or boat to swin in, or rather to sail 

 in, for it was stated to raise aloft its two expanded arms to catch the breeze, and 

 thus to voyage onward. This, for many years, has been proved to be mere fiction. 

 The shell, with which only the female is provided, is of her own manufacture, and 

 she swims just the same as other cephalopods. It is large, not adhering to the 

 body of the animal, but retained in position by the application on the outside of the 

 dorsal pair of arms, which are dilated and especially adapted for the purpose. 

 Whether the argonaut ever quits its shell voluntarily or only by accident is un- 

 known; specimens have been captured at sea without any shell, and they have lived 

 for some time in that condition. A specimen was placed in an aquarium at a time 

 when it was out of its shell. This it re-entered, and remained in it the whole period, 

 about fifteen days, it was in captivity. It invariably swam at the surface of the 

 water with the coiled part of the shell upward, a small portion being above the sur- 

 face, to which the aperture was at right angles or inclined at an angle of 45. It 

 appeared calm and not subject to agitation like the octopus. It remained perfectly 



immovable, for no menace or excitement ap- 

 peared to affect this appearance of tranquillity. 

 Like the octopus, it exhibited chameleon-like 

 changes of the skin, but not so rapidly or with 

 such intensity as that animal. During all the 

 time the specimen lived, all the arms, which 

 have two rows of suckers, were kept within the 

 shell, except the expanded posterior median pair. 

 These, however, were also sometimes drawn 

 within. Four of the arms were bent upward, 

 four downward, leaving the mouth with its 

 parrot-like beak exposed in the middle of their 

 bases. Between the lower or ventral pair of 

 arms the funnel was protruded, by means of 

 which it propelled itself backward. This speci- 

 men was not seen either to walk or swim with 

 its arms; but other observers state that the 

 creature walks or crawls along the bottom like 

 a gastropod, by means of the nonexpanded 



arms, carrying the shell above its body. The eye is round, bordered with black, 

 and the circular pupil is also black. 



The shell is supposed to be secreted chiefly by the palmate arms, aided by the 

 mantle investing the body. It is developed some time after the birth of the argo- 

 naut, and a female has never been seen with a shell before it had attained about an 

 inch in length. The male argonaut is very different to the female, and much smaller, 

 being only about an inch in length. It resembles an ordinary octopus in having neither 

 palmate arms nor shell. The arms are tapering and alike, excepting the third on 

 the left side, which is specialized. This at certain times, having passed through 

 various stages of development, is cast off, and attaches itself to the female, living a 



ARGONAUT. 



