170 CIRRIPEDIA. 



movement of the cirri is made, is the carina, and 

 the opposite one the rostrum; the three interme- 

 diate ones on each side are the carino-lateral, the 

 lateral, and the rostro-lateral valves. Each valve 

 consists of a central portion called the wall, and 

 a portion on each side, which may be either radii 

 or alee, or an ala on one side and a radius on the 

 other. These may be distinguished by the cir- 

 cumstance, that in the overlapping of the parts, 

 the radius is always outside the ala.* 



These terms are very technical, but they are 

 necessary for the discrimination of the Barnacles, 

 which from their nature present peculiar difficul- 

 ties ; and even when theoretical knowledge is per- 

 fect, in many cases it cannot be applied without 

 considerable trouble; the Balanidcn often having 

 their valves so firmly soldered together, that the 

 distinction of radius and ala is altogether oblite- 

 rated. In this case, the specimen must be im- 

 mersed in a boiling solution of caustic potass, 

 when, the animal matter being dissolved away, the 

 valves will separate, and their constituent parts 

 may be recognised. 



Nothing can be conceived more effective, or 

 more beautiful, than the manner in which a Cir- 

 riped obtains its prey. Its food, as Professor 

 Rymer Jones observes, consists of various minute 

 animals, " caught in the water around them by a 

 mechanism at once simple and elegant. Any one 

 who watches the movements of a living Cirriped, 

 will perceive that its arms, with their appended 

 cirri, are in perpetual movement, being alternately 

 thrown out and retracted with great rapidity ; and 

 that, when fully expanded, the plumose and flexi- 



* Darwin's " Monograph of Cirripedia." 



