CEPHALOPODA. 235 



CLASS I. 



CEPHALOPODA. 



THEIR mantle unites under the body, forming a muscular sac which 

 envelopes all the viscera. In several, its sides are extended into fleshy 

 fins. The head projects from the opening of the sac ; it is rounded, 

 furnished with two large eyes, and crowned with longer or shorter 

 conical and fleshy arms or feet, capable of being flexed in every 

 direction, and extremely vigorous, the surface of which is armed 

 with suckers or cups, which enable them to adhere with great tenacity 

 to every body they embrace. These feet are their instruments of 

 prehension, swimming, and walking. They swim with the head back- 

 wards, and crawl in all directions with the head beneath and the body 

 above. 



The Cephalopoda have two branchiae within the sac, one on each 

 side, resembling a highly complicated fern leaf; the great vena cava, 

 having arrived between them, divides into two branches, which pour 

 their contents into two fleshy ventricles, each of which is placed at the 

 base of the branchiae on its own side, and propels the blood into it. 



Respiration is effected by the water which flows into the sac and 

 issues through a funnel placed at its opening. 



Between the base of the feet we find the mouth armed with two 

 stout horny jaws resembling the beak of a parrot. 



These animals are remarkable for a peculiar and intensely black 

 excretion, with which they darken the surrounding water when they 

 wish to conceal themselves. It is produced by a gland, and held in 

 reserve by a sac, variously situated, according to the species. 



Their brain, which is contained in a cartilaginous cavity of the head, 

 gives off a cord on each side, which produces a large ganglion in each 

 orbit, whence are derived innumerable optic filaments ; the eye con- 

 sists of several membranes, and is covered by the skin which becomes 

 diaphanous in that particular spot, sometimes forming folds which 

 supply the want of eyelids. The ear is merely a slight cavity, on 

 each side near the brain, without semicircular canals or an external 

 Meatus, where a membranous sac is suspended which contains a little 

 stone. 



The skin of these animals, of the Octopi particularly, changes colour 



