254 THE ANATOMY OF IXVERTEBRATED ANIMALS. 



to the older naturalists if they failed to discover the affinity 

 connecting the sedentary " Acorn-shells " of a rocky coast 

 with the active Shore-crab which runs among them ; or if 

 they classed the Barnacles with Mollusca, instead of admit- 

 ting them to that place amid the Crustacea which is now 

 assigned to them by every naturalist of competent judgment. 

 Nothing, in fact, at first sight, is less suggestive of a Crusta- 

 cean than a Balanus, or a Lepas y the former firmly fixed 

 by the base of its multivalve conical shell, the latter by its 

 fleshy and contractile peduncle ; the only sign of life in 

 either being the alternate protrusion and retraction, from the 

 valvular opening of the animal's case, of a bundle of curved 

 filamentous cirri, which sweep with a brushing motion through 

 the water, and scoop the floating nutritive matters toward 

 the mouth. 



The valves through which the cirri make their egress are 

 strengthened, in both Balanus and Lepas, by four calcified 

 pieces, two on each side ; those of each half being united to- 

 gether by an oblique suture, or by a regular articulation ; 

 while the two pieces of opposite sides are connected only 

 along one margin, either immediatelj' (Balanus), or by means 

 of an intermediate piece (Lepas). 



The upper, or distal, pieces are termed the terga, the 

 lower, or proximal, pieces the scuta, the intermediate piece is 

 the carina. In Lepas, there are no other hard external 

 pieces; but, in Balanus, the conical shell, into which the 

 valves can be more or less completely retracted, is composed 

 of six portions or compartments. Of these, one is situated 

 on the same side as the opening between the valves and 

 another at the precisely opposite point, or on the same side 

 as the line of union of the valves. The latter is the homo- 

 logue of the intermediate piece, or carina, in Lepms ; the 

 former, in Balanus, consists of three pieces united together, 

 the median rostrum and the two rostro-lateral compartments. 

 On each side of the carina is a compartment termed carina- 

 lateral, and between them and the complex rostrum lies a 

 lateral compartment. 



If the shell consisted of its eight typical pieces (as it does 

 in the genus Octomeris), it w^ould be found that each pre- 

 sented a triangular free middle portion and two lateral wrings. 

 The former is always termed the paries, but the latter re- 

 ceive different names, according as they overlap or are over- 

 lapped by others. In the former case, they are termed radii, 

 in the latter, alee. Thus, typically, the carinal and the ros- 



