396 



COMPARATIVE ANATOMY 



CHAP. 



The straight pedicellarite are far less numerous, and are found scattered over the 

 integument either singly or in groups. 



The three -bladed pedicel lari?e are always found entirely isolated, and may be 

 altogether wanting in some individuals. 



Structure of the straight pedicellarise (Fig. 342, H). Each of the two blades 

 consists of a hollow toothed skeletal piece, which articulates with a common basal 



FIG. 343. A portion of an arm of Asterias stichantha, Sladen, from the lower side (after 

 Sladen). 1, 2, 3, 4, The four longitudinal rows of ambulacral feet ; 5, forficiform pedicellarht 1 ; 0, 

 adambulacral spines ; 7, papulae ; 8, inframarginal spines ; 9, forcipiform pedicellarite at the 

 outer bases of these latter. 



piece. Two muscles serve for opening the pedicellaria, the outer side of each blade 

 being attached by a muscle to the basal piece. The blades are closed by moans 

 of two muscles which run from the inner sides of their bases to the basal piece, 



i. 344. Asterias (Stolasterias) volsellata. Adambulacral plates and neighbouring portion 

 f the oral integument of an arm. /, Straight ; fc, crossed pedicellarite on a cushion at the base of 

 a large spine (a<-) ; m- lt smaller spine (after Sladen). 



and also perhaps by means of two muscles which, lying for the greater part 

 hin the calcareous blades, run from their tips to the basal piece. Each pedi- 

 211am is unrounded by a layer of connective tissue, and covered by body epithelium, 

 in which glandular cells are scattered. 



Structure of the crossed pedicellariae (Fig. 342, K). A crossed pedicellaria 

 t Unlike a forceps with short handles. It also consists of three pieces, the 



