488 THE BARNACLES. 



by a curious shield, composed of two parts, the junction taking place across the centre of 

 the body. Though perfectly harmless, these creatures can be made very offensive, for the 

 natives of Molucca are accustomed to use the long sharp tail spine as the head for an arrow 

 or lance, and thus make a most formidable weapon. Many of these Crustacea attain the 

 length of two feet, so that the spike is nearly a foot in length, and is capable of inflicting a 

 deadly wound. 



The edges of the hinder portion of the shield are deeply toothed, and the space between 

 the teeth is occupied by a rather long and sharply-pointed spine, which is not fixed, but is 

 movable on its basis. The feet are mostly furnished with tolerably strong claws. 



The Molucca Crabs often leave the sea and crawl upon the sand, where they may be 

 taken without much difficulty. They cannot endure the heat of the sun's rays, and are 

 in the habit of burrowing into the sand when the sunbeams beat too fiercely on their shells. 

 Sometimes they do not bury themselves very deeply, and then they are discovered by the 

 projecting tail-spike, which shows itself above the level of the sand, and betrays the position 

 of the animal. As they pass over the sand they present a very curious appearance, as their 

 large shield-like shell entirely covers the limbs, and the creatures seem to be carried along 

 by some external agency rather than to be propelled on their own limbs. Owing to the 

 shortness of the legs, and the large rounded shell, the Molucca Crabs are almost helpless 

 if laid on their backs, being obliged to wait until some friendly wave may strike them and 

 enable them to resume their proper attitude. These crustaceans occur largely in certain 

 strata, and are found in a fossil state, many species attaining to a very great size. One 

 riving species (Limulus cyclops) is a native of the East Indies, and goes by the popular 

 name of PAN-FISH, or SAUCEPAN-CRAB, because the shell, when the limbs and body have 

 been removed and the tail spine permitted to retain its place, has some resemblance to the 

 useful culinary article from which it derives its name. It is often used as a ladle for dipping 

 water out of a vessel. 



BARNACLES; CIRRIPEDIA. 



WE now come to the last members of the Crustacea, creatures which were for a long time 

 placed among the mollusks, and whose true position has only been discovered in comparatively 

 later years. Popularly they are called Barnacles, but are known to naturalists under the 

 general term cirripedes, on account of the cirri, or bristles, with which their strangely 

 transformed feet are fringed. 



When adult, all the cirripedes are affixed to some substance, being either set directly 

 upon it, as the common acorn-barnacle, so plentiful on European coasts ; placed upon a foot- 

 stalk of variable length, as in the ordinary goose-mussel ; or even sunk into the supporting 

 substance, as is the case with the whale barnacles. When young, the cirripedes are free and 

 able to swim about, and are of a shape so totally different to that which they afterwards 

 assume, that they would not be recognized except by a practised eye. More will be said 

 on this subject. 



Along the under surface are set six pairs of limbs not furnished with claws, but being 

 developed at their extremities into two long filaments, jointed and covered with hairs. By 

 means of these modified limbs the cirripedes obtain their food. The common acorn-barnacle 

 affords a familiar and beautiful example of the mode by which this structure is made sub- 

 servient to procuring a supply of food. The closed valves at the upper part of the shell are 

 seen to open slightly, a kind of fairy-like hand is thrust out, the fingers expanded, a grasp 

 made at the water, and the closed member then withdrawn into the shell. 



This hand-like object is in fact the aggregated mass of legs with their filaments. As the 

 limbs are thrust forward, they spread so as to form a kind of casting net ; and as they return to 

 the shell, they bring with them all the minute organisms which were swimming in the water. 

 This movement continues without cessation, as long as the Barnacles are covered with water, 

 and appears to be as mechanically performed as the action of breathing is performed by the 

 higher animals. 



