CKINOIDEA. 



287 



attached by its dorsal apex. The segments of the stalk, which are 

 mostly pentagonal, are connected by bands of tissue, and are pierced 

 by a central canal, which serves for nutrition, and contains a central 

 and five peripheral blood vessels ; at certain distances they bear 

 hollow and segmented cirri, which are arranged in whorls. 



The dorsal surface of the calyx is covered externally by regulai'ly 

 arranged calcareous plates, while the upper (ventral) surface, on 

 which the mouth and -anus are situate, is clothed with a leathery 



FIG. 232. Comatula mediterranea represented from the ventral side. O, moutli ; 

 A, anus. The pinnulas are filled with the generative products. 



.-kin. At the margin of the cup there arise movable, simple or 

 forked, and often branched arms, which are supported by a solid 

 framework consisting of dorsal ly placed calcareous plates, which 

 are movable upon one another by special muscles. In almost 



Arcli. fiir Naturgescli, 1851. W.Thompson, "On the Embryology of the 

 Antedon rosaceus,'" Phil. Trans. Iloi/. Sot-., Tom 155, 1865. W. B. Carpenter, 

 " Researches on the Structure, Physiology and Development of Antedon 

 rosaceus," Ibid., Tom 156. A. Gotte, " Vergl. Entwickelungsgeschichte der 

 Gomatula Mediterranea," Arehlv. fiir michrosk. Anatomie, Tom XU. II 

 Ludwig, " Morphol. Studien an Echinodermen," Leipzig, Ib77. 



