go 



CRUSTACEA CIRRIPEDIA 



as the hard sharp objects which cover rocks and piles near high- 

 water mark on every sea-coast. If we examine the hard slceleton 

 of one of these animals, we find that, unlike the Pedunculata, they 

 possess no stalk, the capitulum being fused on to the surface of 

 attachment by a broad basal disc. Typically, there may be 

 considered to be eight skeletal pieces forming the outer ring which 

 invests the soft parts of the animal, an unpaired rostrum and 



carina, and laterally a 

 pair of rostro - lateral, 

 lateral, and carino-lateral 

 "compartments," as shown 

 in Figs. 60, 63. 



The skeletal ring is 

 roofed over by a pair of 

 terga at the carinal end 

 and a pair of scuta at 

 the rostral end ; these 

 four plates make up the 

 operculum by which the 

 animal can shut itself 



O.M 



B 



St A O G M.C 



Fig. m.—Balanustintmnabulum, with the right half Completely up in its shell, 

 of the shell and of the operculum removed, .^leen qy between the valvCS of 

 from the right side. A, Antennae, the size of 

 wliich is exaggerated ; A.M, addnctor muscle; 

 B, basis ; 0, carina ; Cr, cirri or thoracic appen- 

 dages ; />, oviduct ; <J^ ovary ; L, lateral com- 

 partment ; Lb, labrum or upper -lip ; M^ M, 

 depressor muscles of scutum and terguni ; M.C, 

 mantle-cavity ; 0, orifice of excretory organ ; 

 O.M, opercular membrane ; R, rostrum ; S, 

 scutum ; St, region of stomach ; T, tergnm. 

 (After Darwin.) 



which it can protrude its 

 limbs for obtaining food. 

 Tbe relation of the 

 animal to its shell is 

 shown in Fig. 61. The 

 shell in the Operculata is 



not merely secreted as a 

 dead structure on the external surface of the epidermis, Ijut repre- 



FiG. 62. — Diagrammatic section 

 of the growing shell of Bo.l- 

 anus poTcatus. C, Canals ; 

 Ct, cuticle ; H, hypoderniis 

 ( = epidermis) ; //', part of 

 shell secreted by the hypo- 

 dermis ; HI, hypodermal 

 lamina ; .1/, part of shell 

 secreted by the mantle. 

 (After Gravel.) 



sents a living calciferous tissue interpenetrated by living laminae 



