CEPHALOPODA. 5 



and which frequently support the branchial tissue. They constitute 

 the Pterupoda. 



Others again crawl by means of a fleshy disk on their belly, some- 

 times, though rarely, compressed into a fin, and have almost always a 

 distinct head before. We call these the Gasteropoda. 



A fourth class is composed of those in which, the mouth remains 

 hidden in the bottom of the mantle, which also encloses the branchiae 

 and viscera, and is open either throughout its length, at both ends, or 

 at one extremity only. Such are our Acephala. 



A fifth comprises those, which, also inclosed in a mantle and with- 

 out an apparent head, have fleshy or membranous arms, furnished 

 with cilia of the same nature. We term these Brachiopoda. 



Finally, there are some, which, although similar to the other 

 Mollusca in the mantle, branchiae, &c., differ from them in numerous 

 horny and articulated limbs, and in, a nervous system more nearly 

 allied to that of the Articulata. They will constitute our last class, 

 or that of the Cirrhopoda. 



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 cup$ (a) which enable them to adhere with great 

 tenacity to every body they embrace. These feet are their instru- 

 ments 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 



* M. dc Blainville has changed this name to that of Cephalophora. 



M. de Lamarck at first united my Cephalopoda and Gasteropoda under the* common 

 name of Ccphala, but having subsequently increased the number of classes, he 

 resumed that of Cephalopoda. 



0^7* (a) The original is ccntouses, which means, literally", qupping glasses. ENG. ED. 



