22 STRUCTURE OF THE BARNACLE. 



exchanged for a cone, composed of shelly pieces, accu- 

 rately joined together, and having the base formed of 

 a calcareous plate, closely fixed upon the substance to 

 which the animal is attached. Within this cone the 

 animal lodges, while the pieces that represent the valves 

 of the barnacle, four in number, form a curious oper- 

 culum, or lid, which the animal, by means of certain 

 muscles, can shut at pleasure. The balani, in short, 

 are fixed cirrhopods, lodged in a shelly cone, at- 

 tached by a basal plate to the rock, and capable of 

 being closed by four folding valves above. 



The structure of these creatures requires a few 

 observations. If the two shells of one side of the 

 barnacle be removed, the body of the animal is ob- 

 served to be a soft mass enclosing the viscera, di- 

 lated at its dorsal part, and covered with a delicate 

 membrane, beneath which is a layer of white granular 

 substance. From this body proceed two rows of stems, 

 six in each row, and each of these stems supports two 

 jointed arms, or tentacula, with hair-like appendages 

 springing from each joint, forming a fringe along each 

 fibril. Between the stems on which the tentacula are 

 supported, the body is prolonged into a conical tubular 

 process, which Cuvier regards as the ovipositor of the 

 animal. The mouth is placed on the anterior part 



