ANNULOSA : CRUSTACEA. 



213 



shell itself and the operculum are composed of calcareous 

 plates usually differing from one another in shape, and dis- 

 tmguished by special names. Within the shell the animal is 

 fixed, head downwards. The thoracic segments, six in num- 

 ber, bear six pairs of limbs, each of which consists of a jointed 

 protopodite and a much segmented exopodite and endopo- 

 dite, both of which are ciliated, and constitute the so-called 

 "cirri," from which the name of the sub-class is derived. 

 These twenty-four cirri — the " glass hand " of the £alanus— 

 are in incessant action, being protruded from the opening of 

 the shell, and again retracted within it, constantly producing 

 currents of water, and thus bringing food to the animal. There 

 are no specialised respiratory organs in the family of the £ala- 

 nida. Balani sometimes attain a very considerable size, and 

 Balanus psittacus is largely eaten on the coast of Chili. 



In the Barnacles {Lepadidae, fig. 65, b) the anterior ex- 

 tremity of the animal is enormously elongated, forming with 



Fig. 65.- 



-Morphology of Cirripedia a Sessile Cimpede or Balanoid, Balanus sulccitus. 

 b Pedunculate Cirripede or Lepadoid, Lepas anatlfera. 



the prehensile antennae, the cement-ducts, and their exuda- 

 tion, a long stalk or peduncle, whereby the animal is attached 

 to some solid object. At its free extremity the peduncle bears 

 the " capitulum," which corresponds to the shell of the Bala- 

 noids, and is composed of various calcareous plates, united 

 together by a membrane, moved upon one another by appro- 

 priate muscles, and protecting in their interior the body of the 

 animal with its appendages. The thorax and limbs resemble 

 those of the Balanus; but " slender appendages, which from 

 their position and connections are homologous with the 

 branchias of the higher Crustacea, are attached to, or near to, 

 the bases of a greater or less number of the thoracic feet, and 

 extend in an opposite direction outside the visceral sac." — 

 (Owen.) 

 All the Balanidce are hermaphrodite, and this is also the 



