208 



INVERTEBRATE ANIMALS. 



CHAPTER XXI. 



CEPHALOPODA. 



Class IV. C'EriiALoroDA. 



The last and highest class of the Molhisra is that of the Cephalo- 

 poda, comprising the Cuttle-fishes, Calamaries, Squids, and the 

 Pearly Nautilus. They are all inhabitants of the sea, and are all 



carnivorous ; and they are possessed 

 of considerable powers of locomo- 

 tion. At the bottom of the sea they 

 can walk about head downwards, by 

 means oi the arms (fig. 148) which 

 surround the mouth, which are usu- 

 ally provided with numerous suckers, 

 and which are really produced by a 

 splitting up of the margins of the 

 foot. It is from the presence of 

 these arms that the class derives its 

 name (Gr. hepliale, head ; and podes, 

 feet). The Cuttle - fishes can also 

 swim rapidly, either by means of ex- 

 ])an.sii_)ns of the skin constituting fins, 

 or by the forcible expulsion of water 

 from the cavity of the mantle, the 

 reaction of which causes the animal 

 to move in the opposite direction. 

 The majority of the living Cephalo- 

 pods are naked, possessing only an 

 internal skeleton, and this often a 

 rudimentary one ; but the Argonaut 

 (Paper Nautilus) and the Pearly 

 Nautilus are protected by an external shell, though the nature of 

 this is extremely different in the two forms. 



The body in the Cephalopoda is symmetrical, and is enclosed in an 



Fig. 34S — Sfi'iola Atlantii-n, one of 

 the Cuttle - fishes. (After W.iod- 

 ward.) 



