VIII 



ECHINODERMA TA PEDICELLA RI^ 



397 



two limbs of the forceps, and an intermediate or basal piece, upoii which the 

 blades move. Each limb of the forceps consists of the blade and the stalk or 

 handle. The two limbs cross at the two sides of the intermediate piece like the two 

 parts of a pair of pincers or scissors. "When the two handles are approximated, the 

 pincers close, when they are drawn apart, they open. The opening and closing of 

 the pcdicellaria: is effected by means of six muscles. Two small muscles, running 

 from the outer side of the bases of the blades to the basal piece, by their contraction, 

 open the forceps ; while two pairs of muscles close it. One of these pairs runs 

 within the blades to the basal piece, and the two muscles of the other pair run 

 transversely from the handles of the two limbs to the basal or intermediate piece. 

 An axial strand of elastic fibres run from the stalk of the pedicellaria to the base 



FIG. i>4 5. Pedicellariae of Echinoids. A, Four-bladed pedicellaria of Schizaster canali- 

 fenis (after KceMer). B, Glandular pedicellaria with glandular sacs on the stalk, 

 Sphaerechinus granularis. C, Longitudinal section through a decalcified tridactyle 

 pedicellaria of Centrostephanus longispinus (after Hamann). 1, Adductor muscle ; 2, nerve ; 

 3. elastic column ; 4, calcareous rod ; 5, longitudinal muscle fibres. 



of the forceps. This strand divides into two branches, which embrace its handles. 

 The fibrous strands of the individual pedicellarise penetrate the cushion, which sur- 

 rounds the base of the spine (Fig. 344), and finally break up into fibres which become 

 closely matted together. The whole cushion consists of thickly interwoven fibres of 

 connective tissue and muscle. Muscle fibres run down from the calcareous piece of 

 the spine into the cushion, in which they are lost. By means of these muscles, the 

 cushion can be drawn up the spine, like a sort of sheath. The pedicellarife, like 

 the cushion from which they rise, are covered by a markedly glandular epithelium. 



The three-bladed pedicellariae, apart from the number of their blades, agree in 

 structure with the straight two-bladed pedicellariae. 



3. The pedicellariae of the Echinoidea (Figs. 345 and 346). Pedicellarise occur 

 in all Echinoids on the integument, between the spines, and in one and the same 

 species two or more forms of them may be found. The special arrangement of the 

 various forms of pedicellarife on the body (whether occurring on the ambulacral or 

 on the interambulacral areas, and whether orally or apically), their distribution, 

 number, and very varied form cannot here be described in detail, but must be 

 sought for in systematic works. 



