MOLLUSCA—CIRRIPEDA. 773 
of the mollusca, and seem a species of antenne; 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 bronchize 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 simple intestinal canal; 
a double ovary; anda double winding canal for the passage of the ova. 
The shell of the Cirripeda is always multivalve, or composed 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 por- 
tions, 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 sum- 
mit. 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 portion of the class raised on a tubular pedun- 
cle, which supports the body and 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 shell are isolated or much separated, and do not en- 
tirely cover the body. But, however great the difference between the shells 
of the pedunculated and the sessile species of this class, the animals are 
analogous in point of structure or organization ; and, the shells of both, simply 
attached to the body, or fixed on the sum.nit of the peduncle, are essen- 
tially different from those of the bivalve, where the two pieces of the 
shell are connected by a ligament and hinge. The animals of this class are 
hermaphrodite, and all marine. Lamarck divides the class Cirripeda into 
two orders. 
Order I. PEpuncutata.—Body supported by a tubular moveable peduncle, 
of which the base is fixed upon marine bodies ; mouth almost inferior. 
Order Il. Serssizt1a.—Body destitute of peduncle, and fixed by the shel] 
upon marine bodies: mouth superior and anterior. 
65* 
