90 CRUSTACEA——CIRRIPEDIA CHAP. 
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 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 
=. 6 Leh ae animal can shut itself 
Fic. 61.—Balanus tintinnabulun, with the right half completely up in its shell, 
of the shell and of the operculum removed, seen oy between the valves of 
from the right side. A, Antennae, the size of : : : 
which is exaggerated ; A.M, adductor muscle ; which it can protrude 1ts 
B, basis ; C, carina; Cr, cirri or thoracic appen- limbs for obtaining food. 
dages; D, oviduct; G, ovary; Z, lateral com- - : = 
partment ; Z4, labrum or upper-lip; JM, J, The relation of the 
depressor muscles of scutum and tergum; M.C, animal to its shell is 
mantle-cavity ; O, orifice of excretory organ ; : : : 5 
O.M, opercular membrane; #&, rostrum; S, shown in Fig. 61: "Ehe 
seutum ; Sf, region of stomach; 7, tergum. : s * 
ic ee Bipot eS shell in the Operculata is 
not merely secreted as a 
dead structure on the external surface of the epidermis, but repre- 
Fic. 62.—Diagrammatic section 
of the growing shell of Ba/- 
anus porcatus. C, Canals ; 
Ct, cuticle; H, hypodermis 
(=epidermis); “’, part of 
shell secreted by the hypo- 
dermis ; Hl, hypodermal 
lamina; J/, part of shell 
secreted by the mantle. 
(After Gruvel.) 
sents a living calciferous tissue interpenetrated by living laminae 
