SECT. XI. 



NAKED CEPHALOPODS. 



247 



a fish, the fleshy piston is instantaneously retracted, a 

 vacuum is formed, and the edges of the disk are pressed 

 against the victim with a force 

 equal to the pressure of the 

 superincumbent water and that 

 of the atmosphere. The fish is 

 powerless when embraced by 

 the eight tentacles and their 

 hundreds of suckers; but, if 

 large enough still to struggle, 

 the force is increased by draw- 

 ing in the membranous disk. 

 The Poulpe, the most power- 

 ful of the group which swims 

 far from land, and has to con- 

 tend with large slippery fishes, 

 has a hooked claw in the centre 

 of each sucking-disk, which is 

 clasped into the fish the instant 

 the vacuum is formed. The expansions at the extre- 

 mities of their two long arms, which are thickly and 

 irregularly beset with hooked sucking-disks, not only 

 drag the fish into the embrace of the eight short ten- 

 tacles, but they clasp round it and interlock, so that 

 the fish can be torn to pieces by the parrot-like jaws, 

 and eaten at leisure. The tentacles, long and short, 

 have strong nerves, and a little nerve-mass occupies 

 the centre of each sucking-disk, which gives the ten- 

 tacles great power. 



The sepia, or inky liquid, which all the Naked Cepha- 

 lopoda possess as a means of defence, is secreted in a 

 pyriforin bag, which has an outlet near the respiratory 

 siphon. If the animal be alarmed when devouring its 

 prey, it instantly lets go its hold, discharges the inky 

 liquid into the water, and escapes unseen. 



The skin of this class of animals is thin and semi- 



Fig. 180. Arm of Octopus. 



