CIRRIPEDIA. 155 



tubular and emitting tufts of bristles : these natatory feet strike the 

 water together, and propel the body foi'ward with a jerk : they are 

 aided by the last segment, which is terminated by four setigerous 

 tubercles. 



The antennae probably serve to indicate to the young parasite its 

 appropriate object, to which it then proceeds to attach itself. Tiie 

 second pair of feet increases in size, and the terminal hook enlarges : 

 the feet of the third pair lengthen and unite together to form a 

 cartilaginous circular sucker. The first pair of feet is approximated 

 towards the mouth, and forms the uncinated mandibles. 



The two sexes are alike in their young and locomotive state : the 

 male at its final metamorphosis retains the first pair of feet as man- 

 dibles, very similar in form to those in the female : the second pair 

 is shorter and thicker : the legs of the third jjair always remain 

 separate from each other, and consists usually each of two large 

 joints, the last one terminated by a claw. The posterior natatory 

 feet disappear in both sexes. 



CiRRIPEDIA. 



Many of the Cirripedia are parasitic animals, like the Epizoa, but 

 are dependant upon the organised bodies to which they are attached 

 for their place of residence, not for their food : those species which 

 do not infest other animals are attached to sea-weed, floating timber, 

 or rocks. The Cirripedes are symmetrical animals, with a soft 

 unarticulated body enveloped in a membrane : they are provided with 

 six pairs of rudimentary feet, obscurely divided into three joints, and 

 terminated each by a pair of long and slender many-jointed, ciliated 

 tentacles, curled towards the mouth, and thence giving origin to the 

 name of the class. 



The mouth is provided with a broad upper lip, with two palps or 

 feelers, and three pairs of dentated and ciliated jaws. The opposite 

 extremity of the body is prolonged into a slender many-jointed ciUated 

 caudal appendage, which is traversed by the generative canal. The 

 mouth is situated near the anterior extremity of the body, whicii 

 is modified to form the organ of attachment of the animal. It is 

 sometimes produced to a considerable extent, and is of contracted 

 diameter, forming a long and flexible peduncle ; sometimes it expands 

 at once into a broad disc or basis of adhesion. The Cirripedes are 

 divided according to these modes of attachment into two primary 

 groups, — viz. the pedvinculated, or Lepadoids, and the sessile, or 

 Balanoids. The first are commonly known by the name of Barnacles; 

 the second by that of Acorn-shells. 



