290 



MANUAL OF ZOOLOGY. 



thoracic segments, six in number, bear six pairs of limbs, each 

 of which consists of a jointed protopodite and a much-seg- 

 mented exopodite and endopodite, both of which are bristled, 

 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 Balanus are in incessant action, being pro- 

 truded 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 respi- 

 ratory organs in the family of the Balanidce. Balani some- 

 times attain a very considerable size, and Balanus psittacus is 

 largely eaten on the coast of Chili. 



The remaining family of the Sessile Cirripedes is that of the 

 Verrucidce, comprising only the single genus Verruca. In many 

 respects the Verrucidce. approach the Balanidcz, but the shell is 

 composed of six valves only, and is un symmetrical, whilst the 

 scuta and terga (forming the operculum), though movable, are 

 not furnished with a depressor muscle. 



In the Barnacles (Lepadidce), the anterior extremity of the 

 animal is enormously elongated, forming, with the prehensile 

 antennae, the cement-ducts, and their exu- 

 dation, a long stalk or peduncle, whereby 

 the animal is attached to some solid ob- 

 ject. The peduncle is cylindrical, of vary- 

 ing length, flexible, and furnished with pro- 

 per muscles. In some species it is naked, 

 but in others it is furnished with calcareous 

 scales. At its free extremity the peduncle 

 bears the " capitulum," which corresponds 

 to the shell of the Balanoids, and is com- 

 posed of various calcareous plates, united 

 together by a membrane, moved upon one 

 another by appropriate muscles, and pro- 

 tecting in their interior the body of the ani- 

 mal with its appendages. The thorax and 

 limbs resemble those of the Balanus; 

 but "slender appendages, which from their 

 position and connections are homologous 

 144. Lepas anati- with the branchiae 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 Balanida are hermaphrodite, and this is also the 

 case with most of the Lepadida, but some extraordinary 



Fig 



fera, the common Bar 

 nacle. 



