136 SUCKERS OF THE CEPHALOPODS. 



lar aperture ; but which, when the disc is closely applied 

 to any object, is strongly drawn back, the cavity it filled 

 being now a large vacuum. When the animal releases 

 its hold, it relaxes the contractor muscles of the piston, 

 which returning, fills the vacuum, and the suction 

 ceases. This structure will be readily understood by 

 reference to the annexed diagrams, a shews the ex- 



Suckers. 



panded disc of the sucker, with a central orifice, stopped 

 up by the piston when not in action ; b is a longitudinal 

 section of the sucker at rest, with the piston up to the 

 orifice ; c is a longitudinal section of the sucker in 

 action, showing the piston retracted, and the large 

 vacuum thus produced. 



In some species, the prehensile power of these suckers 

 is still more increased, or, perhaps, rendered more effi- 

 cacious in securing slippery prey, by a strong sharp 

 hook, projecting through the central orifice of each 



