THE BARNACLES. 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 dis- 

 covered 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 

 by 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 {Lhniilns cyclops] is a native of 

 the East Indies,-andgoesby the popular name of PAN-FISH, or SAUCEPAN-CRAB, because 

 the shell, when the limbs and body have been removed and the tail spine per- 

 mitted 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 later 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 

 I'pon it, as the common acorn barnacle, so plentiful on our coasts ; placed upon a foot- 

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

 porting substance, as is the case with the whale barnacles. When young, the cirrhi- 

 pedes 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 be- 

 ing 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 com- 

 mon 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, 



