396 



COMPARATIVE ANATOMY 



CHAP. 



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

 integument either singly or in groups. 



The three -bladed pedicellarine are always found entirely isolated, and may be 

 altogether wanting in some individuals. 



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

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



X- 



FII;. 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 aml>ulaeral feet ; .",, foi ticiform pedicellari;e : u. 

 adambularral spines; 7, papula?; S, inframarginal spines; <i, fore-inform pedicellarui' at the 

 outer liases of these latter. 



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

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

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



FIG. 344. Asterias (Stolasterias) volseUata. Adambulacral plates and neighbouring portion 

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

 a large spine (oc) ; ac\, smaller spine (after Sladen). 



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

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

 cellaria is surrounded by a layer of connective tissue, and covered by body epithelium, 

 in which glandular cells are scattered. 



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

 is not unlike a forceps with short handles. It also consists of three pieces, the 



