772 MOLLUSCA — CIRRIPEDA. 



digestion, applicable to their individual wants, and unconnected with the 

 general nutrition of the common mass. Lamarck divides this class into 

 two orders. 



Order I. Ascidiaeia. — Animals disunited, either isolated, or in groups, 

 without internal communication, and not forming essentially a common 

 aiass. 



Order II. Botkyllakia. — Agglomerated animals, always united, and 

 constituting a mass with a common covering. 



CLASS IV.— CIRRIPEDA. 



Soft animals, destitute of head and eyes, covered with a shell, and fixed ; 

 body iriarticulated, furnished ivith a mantle, and tentacular, cirrous, many- 

 jointed arms above. 



The class Cirripeda forming the genus Lepas, in the system of Linnaeus, 

 was instituted by Lamarck, in 1812, and has since been adopted by Cuvier, 

 Blainville, and other naturalists, as a distinct group of molluscous animals, 

 intermediate between them and the articulated groups. The body in this 

 class is always much shortened, immoveable, and inclosed in a shell, either 

 itself fixed to an extraneous body, or elevated on a tubular and moveable 

 peduncle, which permits some degree of motion. In the first case, the shell 

 adheres immediately to the marine bodies, upon which it is fixed ; while in 

 the other shell, of which the valves are always distinct and moveable, and 

 inclosing the body more or less completely, is raised on a peduncle of greater 

 or less length. This foot-stalk or peduncle is tubular, tendinous, moveable, 

 more or less contractile, and fixed by its base ; and it does not appear that 

 the animal has the power of changing its attachment, or shifting its place. 

 The tunic or mantle of the Cirripeda, in some cases, envelopes only a por- 

 tion of the body, and forms the external coat of the peduncle in those which 

 have a foot-stalk. In others, as in the genera Otion and Cineras, the tunic 

 envelopes all the body, leaving only an anterior opening for the arms. In 

 none is this tunic divided into two lobes, as in the Conchifera and Mollusca. 



The jaws in the Cirripeda are lateral, and along the belly are numerous fila- 

 ments named cirri, disposed in pairs, and composed of a great number of 

 small joints. These cirri forming a kind of arms or fins, vary in number; 

 sometimes there are twenty-four, or twelve pairs on each side. They are 

 long, slender, unequal, and ciliated, with a horny skin. The longest are 

 found at the summit of the body, and they gradually diminish, in such a 

 manner that the shortest are nearest the mouth. In repose, they are rolled 

 up in a spiral form. These cirri or arms have no analogy with the tentacula 



