CEPHALOPODA. 247 



an external Meatus, where a membranous sac is suspended which 

 contains a little stone. 



The skin of these animals, of the Octopi particularly, changes 

 colour in places, by spots, with a rapidity which greatly surpasses 

 that of the Chameleon. 



These animals are voracious and cruel; possessed both of agility 

 and numerous modes of seizing their prey, they destroy immense 

 quantities of Fish and Crustacea. Their flesh is eaten; their ink is 

 employed in painting, and the Indian, or China ink is supposed to 

 be made from it. 



The Cephalopoda comprise but a single order, which is divided 

 into genera, according to the nature of the shell. 



Those which have no external shell, according to Linna3us r form- 

 ed but the single genus. 



SEPIA, Lin. 



Or the Cuttk-fish, which is now divided into a variety of subgenera, the most 

 interesting of which are the two following. 



ABGONAUTA, Lin. 



These Mollusca are always found in a very thin shell, symmetrically fluted 

 and spirally convoluted, the last whorl so large that it bears some resem- 

 blance to a galley of which the spine is the poop. The animal makes a 

 consequent use of it, and in calm weather whole fleets of them may be ob- 

 served navigating the surface of the ocean, employing six of their tentacula 

 as oars, and elevating the two membranous ones by way of a sail. If the 

 sea becomes rough, or they perceive any danger, the Argonaut withdraws 

 all its arms, concentrates itself hi its shell, and descends to the bottom. 



Several species are known, closely resembling each other both in the ani- 

 mal and the shell, which were united by Linnaeus under the name of Argo- 

 nauta argo, or the Paper Nautilus. 



SEPIA, Lam. 



The Sepiae, or Cuttk-fish properly so called, have two long arms and a 

 fleshy fin extending along the whole length of each side of the sac. The 

 shell is oval, thick, convex, and composed of numerous and parallel calca- 

 reous laminae, united by thousands of little hollow columns, running perpen- 

 dicularly from one to the other. This structure rendering it friable, causes 

 it to be employed for polishing various kinds of work; it is also given to 

 birds in aviaries, for the purpose of whetting their beaks. 



NAUTILUS, Lin. 

 In this genus Linnaeus united all spiral, symmetrical and chambered shells, 



