THE BAKNACLES. 645 



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 living 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. 



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

 time placed among the molluscs, and whose true position has only been discovered in 

 comparatively ]ater years. Popularly they are called Barnacles, but are known to 

 naturalists under the general term cirrhipedes, on account of the cirrhi, or bristles, with 

 which their strangely transformed feet are fringed. 



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

 upon it, as the common acorn barnacle, so plentiful on our coasts ; placed upon a footstalk 

 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 cirrhipedes 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 recognised 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 cirrhipedes obtain their food. The common acorn- 

 barnacle of our coasts affords a familiar and beautiful example of the mode by which this 

 structure is made subservient 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 as performed by the higher animals. 



We will now cast a hasty glance at the transformations through which these creatures 

 pass before attaining their perfect state. It has already been mentioned that the young 

 cirrhipedes are free and able to wander about at will ; and as is generally the case in such 

 instances, they are apparently of a higher organization when young than when adult. 

 For example, the young Barnacle can swim freely with certain limbs. When adult, it 

 loses those limbs. When it is young, it possesses eyes ; but when it attains maturity, it 

 loses those valuable organs, which, although indispensable to a wanderer, are needless 

 for a being which is fixed to one spot and needs not to move in order to obtain 

 subsistence. 



When first set free from the parent, the Barnacle is extremely minute, and has a 

 striking resemblance to the young of one of the Entomostraca already described. It has 

 three pairs of legs, with imperfect joints and ending in bristle-like appendages. By the 

 vigorous flapping of these limbs the young Barnacle is driven quickly through the water, 

 with a sharp but uncertain movement. In fact, a microscope of low power, when applied 



