18 



ASTEROIDEA. 



surface of the lobes with thorny prickles. In EcJiinaster they are developed into long 

 defences, and thickly set together on all the surface of the body. In Oreaster (fig. 13) 

 they are thick calcareous pieces, which rise in various forms from the surface of the 

 ossicles. In Astrogonium equestris the smooth spines project from the centre of a nearly 

 circular plate, around the border of which is a circle of granules ; the intermediate spaces 

 are filled with tubercles, among which valve-shaped Pedicellarise are scattered (fig. 8). 

 Besides the spines disposed on the sides and upper surface of the rays, there are others 

 which, in general, have a very regular arrangement, and form consecutive rows on each 

 side of the ambulacral valleys. 



The granules are fine, calcareous, wart-like processes, which grow from the surface of 

 the integument, and cover all the rays in Ophidiaster and Scytasier. In other genera 

 they are much more limited in their distribution, and occupy the inter-spinous spaces on 

 the surface of the rays. 



Thepawilla are formed of processes of the integument, which rise like short stems in 

 regular order from the surface of the ossicules ; each stem caiTies a crown of short, bristly 

 spines, as in Solaster (fig. 4). In Scytaster they are distributed over the discal membrane, 

 and arranged in lines on the sides and upper surface of the rays. In Astropecten (fig. 3), 

 Luidia (fig. 6), Ctenodiscus, and Archaster, they fill the entire space on the upper surface 

 within the area circumscribed by the marginal plates. 



The PedicellaricB are small, pincers-like bodies, supported on slender, flexible stems, 

 and found in considerable numbers around the bases of the spines and on the membrane 

 surrounding the mouth. They w^ere first observed by Miiller^ on the test of a sea-urchin 

 {Echinus splmrd), and described by him as Epizoa. Lamarck^ classed them with the 

 Polypes, and Cuvier^ doubtfully adopted the same view, as also Schweigger;* whilst Munro, 

 Oken, Delle Chiaje, Sharpey, Valentine, Sars, Miiller and Troschel, and Porbes considered 

 them as tegumentary appendages of the animals on which they are found. 



In Uraster ruhens, Lin., groups of these pedicellated, pincers-like bodies are seen clus- 

 tering around the base of the spines, each consisting of a membranous stem, surmounted 

 by a pair of calcareous forceps not unlike the miniature claw o£ a Crustacean ; when alive 

 and active, if a fine needle is introduced between their expanded blades, they close upon 

 the foreign body, and grasp it with force. Professor Porbes^ examined the Pedicellaria 

 in this star-fish, and observed that " those on the body and upper spines difler in shape 

 from those on the spines which are arranged on the sides of the ambulacral valleys. The 

 former are much shorter and blunter in their blades than the latter. The calcareous 

 forceps of which their heads consist are imbedded in an integument of a soft, granular 



1 ' Zoologia Danica.' 



2 'Animaux sans Vertfebres,' 1st ed., vol. ii, p. 63. 

 2 ' Regne Animal,' 2d ed., vol. iii, p. 297. 



* ' Handbuch der Naturgeschichte.' 



^ ' History of British Star-fishes,' p. 98. 



