CEINOIDEA. 



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 regularly 

 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, mouth ; 

 A t anus. The pinnulae are filled with the generative products. 



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

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

 framework con-isting of dersally placed calcareous plates, which 

 are movable upon one another by special muscles. In almost 



Arch, filr Naturgetcli, 1851. W.Thompson, "On the Embryology of the 

 Antedon rosaceus," Phil. Trans. Roy. Soc., TJom 155, 1865. W. B. Carpenter, 

 " Researches on the Structure, Physiology and Development of Antedon 

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



Sematula Mediterranea," Archiv. fur mickrosTt. Anatomic-. Tom XII. H 

 Ludwig-, "Merphol. Studien an Echinodermen," Leipzig, It 7 7. 



