CIRRIPEDIA. 



237 



grown specimens on rooks and stones. In this stage 

 the valves of the shell and of the operculum were 

 visible, as well as the movements of the arms of the 

 contained animal, although these last were not yet 

 completely developed. The eyes, also, were still 

 perceptible, but these gradually disappear with the 

 increasing opacity of the shell; and the animal be- 

 comes blind for the remainder of its life. Thus, then, 

 a creature originally free, capable of swimming 

 about, and furnished with distinct organs of sight, 

 becomes permanently and immoveably fixed, and its 

 optical apparatus obliterated. 



The Cirripedes are divided into two families. 



The Barnacles (Lepas\ (Fig. 181) are always found attached to 

 some foreign substance by a long flexible peduncle, which pos- 



FlG. 181. BAP.KACLEs. 



scsses great power of contraction. Each valve of their shell is 

 usually composed of two triangular pieces, and is closed at the 

 back by an elongated plate, so that the whole shell consists of five 

 pieces. They are very widely disseminated, and adhere to submarine 



