162 



THE HARMONIES OF NATURE. 



All the cephalopoda are marine animals, and breathe through 

 branchiae or gills. These organs are concealed under the mouth 



Cuttle -fish. (Sepia.) 



in a cave or hollow, which alternately expands and contracts, 

 and communicates by two openings with the outer world. The 

 one, in form of a slit, serves to receive the water; the other, 

 which is tubular, is used for its expulsion. 



According to the different number of their branchiae, the eepha- 

 lopods are divided into two natural groups, one with four, the 

 other with two gills. The former, which abounded in the primi- 

 tive ocean, is reduced in the present seas to the single genus 



of the Nautili; the latter, which 

 is far more numerous, is subdi- 

 vided into the two great families 

 of the octopods and the decapods; 

 the former having only eight sessile 

 feet, the latter ten, two of which 

 are considerably longer than the 

 rest. The feet are studded on the 

 inner surface with acetabula or suck- 

 ers, either sessile or pedunculated. 

 The sessile cups of the octopods are 

 muscular disks with a soft and tumid 

 margin (e), and a circular aperture in 

 the centre (#), opening into a cavity 

 which widens as it descends, and con- 

 tains a cone of soft substance rising 

 from its bottom like the piston of a 

 syringe. When the sucker is applied to a surface for the purpose of 

 adhesion, the piston, having previously been raised so as to fill the 



Section of an Arm and Suckers 

 of a Poulp. 



