MOLLUSCA — CIRRITEDA. 773 



of the mollusca, and seem a species of antennae ; 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 bronchiae.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 ; and a 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 summit 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. Pedtjnculata. — Body supported by a tubular moveable peduncle, 

 of which the base is fixed upon marine bodies ; mouth almost inferior. 



Order II. Sessilia. — Body destitute of peduncle, and fixed by the sheil 

 upon marine bodies : mourn superior and anterior. 



65* 



