BARNACLES. 281 



washed into the mouth that lies below them. The abdomen is undeveloped ; but 

 the rest of the body is enveloped in a fold, or mantle, supporting- the outer shelly 

 skeleton. The jaws consist of two pairs of maxillae, and a pair of mandibles, and 

 the lower part of the head is inferiorly continued into the stalk, which contains 

 the gland secreting the cement. If a barnacle be carefully removed from its point 

 of attachment, the remains of the first pair of antennae may be observed on the 

 adhesive surface. When first hatched, the young are in the Nauplius stage, being 

 furnished with a median eye, and three pairs of appendages, of which the posterior 

 two are branched. After swimming for a while by means of these appendages, 



BARNACLES ATTACHED TO PUMICE. 



the larva moults several times, and passes into a second stage, in which, with its 

 two eyes and compressed carapace, it resembles a Daphnia. The rudiments of the 

 six pairs of thoracic legs appear behind the mouth, and the first pair of swimming 

 appendages become antenniform, each being provided with a sucker. By means 

 of these suckers the larva fixes itself to its permanent resting-place, and, the cement- 

 gland pouring out its secretion, glues the creature firmly to its point of attachment. 

 Hence it follows that the fixed end of the stalk is the front extr< mity of the body. 

 In the allied stalkless barnacle (Megalasma) the shell is attached directly to the 

 support. We are thus led on to the acorn-barnacles (Balanus), in which the entire 

 animal is enclosed in a shell formed originally of six pieces, which grow into a 

 tube of variable length. Some of the latter group (Balanidce), namely, the genus 



