NAUTILUS A^S^D AMMONITE. 73 



of knowledge might be worth something to you if you could 

 breathe under water; and he may teach you how to swim, 

 but not how to sail, for in spite of all poetic theories, he 

 does the former and not the latter. Most usually he walks 

 about at the bottom of the sea on his long arms, something 

 like the Cuttle-fish, feeding on the marine vegetation; the 

 shell is then uppermost; if we could look inside of it we should 

 see numerous little chambers or cells, the larger and outermost 

 of which only are inhabited by the mollusk, the others being 

 filled with air render the whole light and buoyant. Through 

 the centre of these chambers, down to the smallest of them, 

 runs a membranous tube which can be exhausted or filled 

 with fluid at the pleasure of the animal, and the difi'erence 

 thus effected in the weight of the shell enables it to sink 

 or swim; in the latter case, up it goes to the sui'face, and 

 ''keel upwards from the deep," emerges, as the poet has said, 

 but once there it soon reverses its position. The shell becomes 

 like a boat it is true, but its inhabitant neither points a sail 

 nor plies the oar, but propels itself along stem foremost by 

 a muscular action, which by alternately compressing and 

 loosening a kind of siphon, throws out jets or gushes 

 of water, which by the resistance they meet with from the 

 surrounding fluid, give the desired onward motion, and away 

 the swimmer goes, his long arms gathered closelj^ together, 

 and streaming behind like the tail of a comet, and its round 

 eyes keeping a sharp look out on either side. Should it espy 

 danger, the body and limbs are withdrawn into the shell, and 

 the fluid diiven through the central tube, so as to compress 

 the air in the pearly cells, and down sinks the swimmer once 

 again to his native depths, where 



"The floor is of sand like the mountain drift, 



And the pearl shells' spangle the flintj- snow; 

 And from coral rocks the sea-plants lift 

 '' Their boughs where the tides and billows flow, 



The water is calm and still below. 

 For the winds and waves are absent there; 



And the sands are bright as the stars that glow 

 In tlie motionless fields of upper air. 

 And life in rai-e and beautiful forms, 



Is sporting amid those bowers of stone, 

 And is safe, when the wrathful spirit of storms, 



Has made the top of the waves his own." 



