Common Starjish. 229 



of the Asteroidea as invalidating', pro tanto, Midler's dictum, 

 that this latter class alone of Echinodermata possesses an 

 internal skeleton, see Semper, Reisen in Archipel des Philli- 

 piden, Theil. ii., Hffc. iv., p. 162 ; see also Wrig-ht, British Fossil 

 Echinodermata of the Oolitic Formations, Palaeontog-raphical 

 Society's Memoirs, 1862, vol. ii., p. 14. For a comparison of 

 the osseous skeleton of Asterias {Uraster) rnbens with that of 

 a fossil species from the Middle Lias, Uraster Gavei/i, Forbes, 

 see Wrig-ht, I. c, p. 100, pi. i. 

 For an account of the Pedicellariae, see Sars cit. Wright, I. c, 

 p. 19. The pedicellariae of the Asteriae and Echinoidea are 

 not homologous with the avicularia of the Polyzoa, to which 

 they bear a considerable resemblance. The pedicellariae are 

 modified spines; the avicularia are specially modified or poly- 

 morphic individuals of the compound Polyzoan colony. The 

 two sets of structures appear however to be analogous, being 

 both alike prehensile organs. 



