CEPHALOPODA. 



25 



power of discharging from their bodies when danger ap- 

 proaches, is another curious provision for their safety ; by- 

 its means they discolour the water around them, and thus 

 elude their enemies, probably immediately after the dis- 

 charge, darting off in a contrary direction with great speed. 

 The animals of the genus Nautilus do not seem to pos- 

 sess this wonderful resource in times of danger, as they 

 can retire into their strong shelly covering. " The deep 

 brown colour, sepia, and the darker pigment, Indian ink, 

 are the prepared fluid of the ink bags of different species 

 of cuttle fish ; a similar substance, secreted by extinct 

 naked Cephalopoda, is found in a fossil state." (Mantell.) 



The Cephalopoda are divided into two great orders — 

 Dibranchiata — the animals of which have two branchia ; 

 and Tectibranchiata — the branchia being four. 



Order I. 



DIBRANCHIATA. (Owen.) 



The animals of this order have two branchia (whence the 

 name), large immovable eyes, eight or ten arms covered 

 on the inner side with suckers, which sometimes have the 

 character of claws ; a thick and fleshy mantle, having but 

 one opening ; an ink bag and the sides of the funnel or 

 vent tube entire ; from this tube they can forcibly eject 

 the water which has served the purposes of respiration ; 

 this is effected by a contraction of the body, giving them, 

 at the same time, a powerful backward movement. 



Section I. — Octopoda. 



The animals have the eight arms arranged round the 

 mouth, and beset with suckers. 



