CRUSTACEA CIRRIPEDIA 



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 find that, unlike the Pedunculate, they 

 possess 110 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 

 A o G M.C animal can shut itself 



FIG. Ql.Balanustintinnabulum, with the right half completely Up in its shell, 



of the shell and of the opercuhun removed, seen QJ> between the Valves of 



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



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



B, basis ; 0, carina ; Or, cirri or thoracic appen- li m bs for obtaining food. 



dages ; D, oviduct ; G, ovary ; L, lateral com- . 



partment; Lb, labrum or upper - lip ; M, M, -Lhe relation ot the 



depressor muscles of scutum and tergum ; M.C, animal to its shell is 

 mantle-cavity ; O, ontice of excretory organ ; 



O.M, opercular membrane; R, rostrum; S, shown in Fig. 61. The 



scutum ; St, region of stomach ; T, tergum. ghell in the Qperculata is 



not merely secreted as a 

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



(After Darwin.) 



FIG. 62. Diagrammatic section 

 of the growing shell of BaJ- 

 anus porcatus. G, Canals ; 

 Ct, cuticle ; H, hypodermis 

 ( = epidermis) ; H', part of 

 shell secreted by the hypo- 

 dermis ; HI, hypodermal 

 lamina ; M, part of shell 

 secreted by the mantle. 

 (After Gruvel.) 



sents a living calciferous tissue interpenetrated by living laminae 



