MONOGRAPH OF THE EXISTING CRINOIDS. 



167 



internal body septum; the firet arm plates (radials) eonstitute the entire cah-x. 

 Resting upon these first arm plates and the arm bases is the large visceral mass, 

 more than half of the total area of which is exposed. 



Fig. 104.— Lateral view of a specimen or Asiedon buida from PLYMOcin, Enolanii, sHowisa the relathe propor- 



TIONS OF THE ARMS, PCnTOLES, CENTRODOESAL, AND CIRRI, AND THE INTERPRUIIBEACHIAL PLATES. 



In the majority of the holothurians the calrareous plates other than diffuse 

 spicules are wholly internal, and the entire body wall is soft. 



The crinoidal columnals have the same ultimate origin as the calj-x plates; 

 but they arose, not directly from an aggregation of spicules nii.l jilatos, but sec- 



