METAMORPHOSES. 397 



an ample shield, terminating anteriorly in two ex- 

 tended horns, and posteriorly in a single elongated 

 spinous process ; and, what is stranger still, a large, 

 conspicuous eye, of which no vestige is traceable in 

 the adult. 



It still remains uncertain how long the larvae of 

 these Cirripedes remain in this, their first and free 

 state, but it is probably for a longer or shorter period 

 of time, according as they sooner or later meet with 

 a support adapted to their respective habits. How- 

 ever this may be, sooner or later a second change 

 of form takes place, quite as remarkable as the first ; 

 and the young Barnacle makes its appearance under 

 a totally different aspect (PL VII. fig. 6, b). 



The little creature in this condition is quite trans- 

 lucent, one-tenth of an inch long, of a somewhat 

 elliptic form, and of a brownish tint. When in a 

 state of perfect repose, it resembles a very minute 

 mussel, and lies upon one of its sides at the bottom of 

 the vessel of sea-water in which it is placed. At this 

 time all the members of the animal are withdrawn 

 within the shell, which appears to be composed of 

 two valves, united by a hinge along the upper part of 

 the back, and capable of opening from one end to the 

 other along the front, to give occasional exit to the 

 limbs. These are of two descriptions : viz. anteriorly, 

 a large and very strong pair, provided with a cup-like 

 sucker and hooks, serving solely to attach the embryo 

 to rocks, stones, &c. ; and posteriorly, six pairs of 

 natatory members, so disposed as to act in concert, 

 and to give a forcible stroke to the water; thus causing 

 the animal, when swimming, to advance by a sue- 



