CRUSTACEA CIRRIPEDIA 



CHAP. 



AM 



O.M 



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

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

 of one of these animals, we tind 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 carina 1 end 

 and a pair of scuta at 

 the rostral end ; these 

 four plates make up the 

 operculum by which the 

 o u M.C animal can shut itself 



FIG. 61.Balanustinti>mabulnm, with the right half Completely up ill its shell, 

 of the shell and of the operculum removed, seen QJ- between the valves of 

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



winch is exaggerated ; A.M, adductor muscle ; Which it Can protrude its 

 B, basis ; 0, carina ; Or, cirri or thoracic appen- li m lj S f or obtaining food, 

 dages ; l>, oviduct; df, ovary; /,, lateral com- 

 ]>artment ; Lb, labrum or upper-lip; M, M, 

 depressor muscles of scutum and tergum ; M.<\ 

 mantle-cavity ; 0, orifice of excretory organ ; 



O.J/, operenlar membrane; R, rostrum; ,S', sllOWll ill Fig. 61. The 

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

 (After Darwin.) 



IV! 



B 



The relation of the 

 to its shell is 



shell in the Operculata is 

 not merely secreted a;s ;i 

 (lend structure <>n the external surface of the epidermis, but repre- 



FIG. <>-. Diagrammatic section 

 of tlie growing shell of /lul- 

 anus porcatus. ", i 'anals : 

 Ct, rntic],. ; //, liypodermis 

 ( = epidermis) ; //', part of 

 shell secreted by the hypn- 

 dermis ; HI, hypodermal 

 lamina ; J/", part of shell 

 secreted by the mantle. 

 (After Gravel.) 



--HI 



sents a living calciferous tissue interpenetrated by living laminae 



