30 ORGANS OF SUPPORT, 



an inner muscular coat, so that it is capable of rapidly 

 contracting when alarmed. The dorsal shell e, is the only 

 piece placed on the median plain, and grows by layers added 

 to its inner surface and increasing successively from the 

 proximal to the distal extremity. The larger lateral pieces, 

 c, c, to which the animal is fixed by a strong transverse 

 muscle of attachment, as in bivalved mollusca, grow likewise 

 by layers extended from the whole of the distal margin, the 

 centre of ossification being at the proximal point. The two 

 distal smaller opercular pieces d, grow from their distal to- 

 wards their proximal ends. From their greater extent of 

 motion by means of their long fleshy peduncle, these le- 

 pades do not require to possess external shells so strong as 

 the fixed sessile balani. A dorsal view of the same shell on 

 a more reduced scale is given in Fig. 1 3, 2, which represents 

 the direction of the successive layers of growth of the dorsal 

 plate , which is analogous to the whole complex cone of the 

 balani, the four lateral moveable pieces representing the four 

 valvular small pieces in the sessile species. In Fig. 13, 3, 

 the tubular peduncle is divided to show its outer coriaceous 

 covering k, and the inner muscular coat /, with the inter- 

 posed skin i, and the right side of the shell is removed to 

 show the inverted and curved position of the animal in its 

 cavity. In some of the pedunculated cirrhopods, as the 

 poUicipes, there are several small supplementary calcareous 

 pieces placed at the junction of the peduncle with the base 

 of the shell, and some, as the cineras, have only a cartilage- 

 nous or membranous covering unconsolidated by calcareous 

 pieces. The anterior part of the body (Fig. 13, 3, ,) of this 

 enclosed animal, as in most other articulata, has less of the 

 articulated appearance, less distinct segments than the pos- 

 terior portion of the trunk, and the skin of that anterior part 

 is here thin and membranous. The abdominal, or posterior 

 portion of the body (Fig. 13, 3, b, c,) is that tapering articu- 

 lated, and free part, from the sides of which the articulated 

 cirrhated and pedunculated members project. The muscles 

 by which the anterior bulbous part of the trunk is attached 

 to the valves of the shell are seen at y, and the strong 

 adductor muscle passing across from the right to the left 

 valve, and by which they are firmly closed when the animal 

 is alarmed, is seen at/. The six thick muscular peduncles 



