306 MOLLUSC A. 



CLASS I. 



CEPHALOFODA(l). 



Their mantle unites under the body, forming a muscular sac 

 which envelopes all the viscera. In several, its sides are extend- 

 ed 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, ca- 

 pable of being flexed in every direction, and extremely vigor- 

 ous, 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, 

 natation, and walking. They swim with the head backwards, 

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

 above. 



A fleshy funnel placed at the opening of the sac, before the 

 neck, affords a passage to the excretions. 



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 ven- 

 tricles, each of which is placed at the base of the branchiae on 

 its own side, and propels the blood into it. 



The two branchial veins communicate with a third ventricle, 



(1) M. de Blainville has changed this name to that of Cephalophora. 



M. de Lamarck at first united my Cephalopoda and Gasteropoda under the com- 

 mon name of Cephala, but having subsequently increased the number of classes, 

 he resumed that of Cephalopoda. 



