122 CIRIUPEDA. 



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 filaments 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, un- 

 equal, 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 to the mouth. In repose 

 they are rolled up in a spiral form. These cirri or arms have 

 no analogy with the tentacula of the mollusca, and seem a spe- 

 cies of antennas ; but as the animal has no head, M. Lamarck 

 considers them as arms. 



The heart in this class is situate towards the back, and the 

 branchiae on the sides. Their nervous system forms a series of 

 knots or ganglions under the belly. The animals are placed in 

 their shell in such a manner that the head is below, and the 

 cirri towards the orifice. Between these is a long fleshy tube, 

 at the base of which, towards the back, is the anal opening. In 

 the interior is the stomach, with a number of small cavities in 

 its walls, which appear to fulfil the functions of a liver ; a sim- 

 ple intestinal canal ; a double ovary ; and a double winding ca- 

 nal for the passage of the ova. 



The shell of the Cirripeda is always multivalve, or compos- 

 ed of a number of separate pieces. In a great portion of the 

 class, however, where the shell is fixed immediately to other 

 bodies, the shell appears univalve, its portions, six in number, 

 being generally joined together at the sides. This shell is 

 conical or tubular, fixed by its base, truncated and open at the 

 summit. In the opening, which is terminal, are two or four 

 moveable valves, which the animal opens and shuts at will, and 

 which form what is termed the operculum. But in that por- 

 tion of the class raised on a tubular peduncle, which supports 

 the body and the shell, the shell is distinctly multivalve, and 

 of a different character from the sessile species. In the greater 

 number this shell consists of five unequal pieces, which form, 

 when the shell is shut, a cone compressed on the sides ; in one 

 genus, besides these five principal pieces, are found others much 

 smaller, termed accessory pieces ; and in others the pieces of the 



