270 



MANUAL OF ZOOLOGY. 



man tie- sac, and there are two or four plume-like gills within 

 the mantle. There is an anterior tubular orifice (the ' infun- 

 dibuluin' or 'funnel'), through which the effete water of re- 

 spiration is expelled. The flexure of the intestine is neural. 



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 carnivo- 

 rous, and are possessed of considerable locomotive powers. At 

 the bottom of the sea they can walk about, head downwards, 

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

 are usually provided with numerous suckers or 'acetabula.' 



They are, also, enabled to swim, 

 partly by means of lateral ex- 

 pansions of the integument or 

 fins (not always present), 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, pos- 

 sessing only an internal skele- 

 ton, and this often a rudimen- 

 tary one ; but the Argonant 

 (Paper Nautilus), and the 

 Pearly Nautilus, are protected 

 with an external shell, through 

 the nature of this is extremely 

 different in the two forms. 



The integument in the Cuttle- 

 fishes is provided with nume- 

 rous little sacs, containing pig- 

 ment-granules of different colours, and termed ' chromato- 

 phores.' By means of these many species can change their 

 colours rapidly, under irritation or excitement. 



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

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

 tion of the mantle of the other Mollusca. Ordinarily there is 

 a tolerably distinct separation of the body into an anterior ce- 

 phalic portion (prosoma), and a posterior portion, enveloped 

 in the mantle, and containing the viscera (metasoma). The 

 head is very distinct, bearing a pair of large globular eyes, and 

 having the mouth in its centre. The mouth is surrounded 

 by a circle of eight, ten, or more, long muscular processes, or 

 ' arms,' which are generally provided with rows of suckers. 



Fig. 82. Cephalopoda. Loligopsis, a 'de- 

 capod' Cuttle-fish. 



