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 Fioh 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 Linnaeus, form- 

 ed but the single genus. 



Sefia, Lin. 

 Or the Cuttle-fish, which is now divided into a variety of subg'enera^ the most 

 interesting of which are the two following'. 



ABooNArTA, 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 tlie 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 ai'ms, concentrates itself in its shell, and descends to tlie bottom. 



Several species ai-e known, closely resembling each other botlv in the ani- 

 mal and the shell, which were united by Linnaeus under tlie name of ^go- 

 nauta argo, or the Paper Nautilus. 



Sei'ia, Lam. 

 The Seplae, or Cuttle-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, tliick, convex, and composetl of numerous and parallel calca- 

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

 dicularly from one to tlxe 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 Liimseus united all spiral, symmetrical and chambered shells. 



