THE SEPIA. 691 



I'ng attentively all that passed around it. The slender arms were folded 

 back from their base and inserted very deeply round the body of the 

 poulp, in such a manner as to fill in part the empty spaces which the 

 head must naturally leave in the much larger opening of the shell." 



Mr. Rang then proceeds to show the real use of the expanded arms, 

 which is to cover the shell on its exterior, and, as has since definitely 

 been proved, to build up its delicate texture and to repair damages, 

 the substance of the shell being secreted by these arms, and by their 

 broad expansions moulded into shape. 



The modes of progression employed by the Argonaut are to the full 

 as wondrous as its fabled habits of sailing. Its progression by crawl- 

 ing has already been cas- 

 ually mentioned. While 

 thus engaged the creature 

 turns itself so as to rest on 

 its head, withdraws its body 

 as far as possible into its 

 shell, and, usiup^ its arms . ^ 



n., 1 °1 1 1 X ArGONAUTA PaPYRACEA, SWIMMING. 



like legs, creeps slowly but ' 



securely along the ground, sometimes affixing its discs to stones or pro- 

 jecting points of rocks for the purpose of hauling itself along. 



When, however, it wishes to attain greater speed and to pass through 

 the wide waters, it makes use of a totally different ptinciple. 



As has already been mentioned, the respiration is achieved by the 

 passage of water over the double gills or branchiae, the water, after it 

 has completed its purpose, being ejected through a moderately long 

 tube, technically called the siphon. The orifice of the siphon is di- 

 rected toward the head of the animal, and it is by means of this simple 

 apparatus that the act of progression is effected. When the creature 

 desires to dart rapidly through the water it gathers its six arms in a 

 straight line, so as to afford the 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. 



As the various cephalopods are so numerous as to preclude all possi- 

 bility of figuring and describing each species, we must therefore content 

 ourselves with a general account of the members of each family. 



The common Sepia of our own seas is chiefly remarkable for the 

 chalky internal skeleton, commonly called cuttle-bone, and much used 

 for the manufacture of tooth-powder. This year (1875) I found eight 

 of these bones on the sands at Margate, and all within a space of a few 

 yards square. 



The AVp:bbed Sepia is an inhabitant of Greenland, and very rare. 

 Its color is violet. 



