CEPHALOPODA. • 5 
and which frequently support the branchial tissue. They constitute 
the Pteropoda. 
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 arc 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 ciip^{a') Avhich enable them to adhere Avith great 
tenacity to every body they embrace. These feet are their instru- 
ments of prehension, natation, and Avalking. They SAvim Avith the 
head backAvards, and craAvl in all directions Avith the liead 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 tAVO branchlse Avithin the sac, one on each 
* M. de Blainville has changed this name to that of Cephalophora. 
M. de Lamarck at first united my Cephalopoda and Gasteropoda under the common 
name of Cephala, but having subsequently increased the number of classes, he 
resumed that of Cephalopoda. 
( a) The original is veniouses, which means, literally, cupping glasses. — E xg. Ed. 
