224 



PHYLUM ECHINODERMATA. 



There are no special organs of sense, but sensory cells are scattered among 

 the ciliated ectoderm cells on the inner sides of the blades. 



(3) The ophicephalous pedicellariae, which are distributed all over the 

 shell and on the buccal membrane, are smaller than the preceding. The 

 stalk contains a calcareous rod proximally and an elastic band distally in 

 the axis, and the blades, which are short and broad and toothed along the 

 edges (not shown in the figure), carry at the base a calcareous semicircular 

 rod which crosses those of the two other blades and ensures a good arti- 

 culation (Fig. 167, 2). The blades are without glands and patches of 

 sensory epithelium, but there are sometimes mucous glands on the stalk 

 in the Diadematidae. These glands may be much developed and the 

 blades reduced, in which case they approximate to the globifer condition. 



FIG. 166. Pedicellariae of Echinoids. A, 4-bladed pedicellaria of Schizaster canaHferus ; 

 B globiferous pedicellaria of Sphaerechinus granularis with glands on the stalk ; C longi- 

 tudinal section of a decalcified tridentate pedicellaria of Centrostephanus longispinus. 

 1 adductor muscle ; 2 nerve ; 3 elastic column ; 4 calcareous rod ; 5 longitudinal muscular 

 fibre (from Lang). 



(4) The triphyllous pedicellariae are the smallest kind and have short 

 broad leaf-like blades without teeth or with very fine teeth (Fig. 167, 4). 

 The stalks are very flexible, the calcareous stalk only reaching half way 

 and being continued by elastic tissue. They are without glands and 

 special sense organs. 



The function * of pedicellariae is to seize upon foreign bodies 

 or organisms which approach or touch the shell and spines. 

 The globiferous pedicellariae by means of their poison glands 

 are probably able to deal with the more powerful organisms. 



* J. von Uexkiill, Zeitsch. f. Biol. (2), 19, 1899, p. 334. 



