53 



CHAPTER XXVII. 



CLASS CEPHALOPODA. 



Class IV. Cephalopoda. — The members of the Ceijhcdopoda 

 are defined by the possession of eight or more arms 'jplaced in 

 a circle round the mouth ; the hody is enclosed in a muscular 

 mantle-sac, and there are tico or four plume-like gills loithin 

 the mantle. There is an anterior tubular orifice (the "infundi- 

 huhviii " or "funnel"), througli which the effete water of respira- 

 tion is expelled. 



The Cephalopoda, comprising the Cuttle-fishes, Squids, 

 Pearly Nautilus, &c., constitute the most highly organised of 

 the classes of the Mollusca. They are all marine and car- 

 nivorous, and are possessed of considerable locomotive powers. 

 At the bottom of the sea they can walk about, head down- 

 wards, by means of the arms which surround the mouth, and 

 which are usually provided with numerous suckers or '-'aceta- 

 bula." They are also enabled to swim, partly by means of 

 lateral expansions of the integument or fins (not always pres- 

 ent), and partly by means of the forcible expulsion of water 

 through the tubular " funnel," the reaction of which causes 

 the animal to move in the opposite direction. 



The majority of the living Cephalopods are naked, possess- 

 ing only an internal skeleton, and this often a rudimentary 

 one ; but the Argonaut (Paper Nautilus) and the Pearly 

 Nautilus are protected with an external shell, though the 

 nature of this is extremely different in the two forms. 



The body in the Cepludopoda is symmetrical, and is en- 

 closed in an integument which may be regarded as a modi- 



