286 



ECniNODEEMATA. 



depths. Many possess a great reproductive power, and are able to 

 replace lost parts, such as arms, with all their apparatus of nerves 

 and sense organs. 



CLASS I. CEIXOIDEA* 



Globular or cup-shaped E chinodermata with segmented arms fur- 

 nished with pinnulce. They are, usually attached by a segmented 



calcareous stalk. The 

 skin upon the aboral 

 side is provided with 

 plates, the ambulacral 

 appendages have, the 

 form of tentacles, and 

 are situated in the 

 ambulacral furrows of 

 the calyx and of t'he 

 segmented arms. 



The greater number 

 of Crinoidea are cha- 

 racterised by the pre- 

 sence of a segmented 

 stalk bearing cirri. 

 This stalk arises from 

 the apical (dorsal) pole 

 of the calyx, and is 

 attached at the in- 

 ferior end to surround- 

 ing objects (fig. 231). 

 In some few living- 

 genera, as Comatida 

 (fig. 232) and Actino- 



thls Stalk ^ 



FIG. ZSl.-Pentacrinu, caput Medvsv (after J. Miiller). 



O, mouth ; A, anas, of the disc, which is represented from Only present ill the 



the oral side. young form. The body 



with the contained viscera appears, therefore, as the calyx at the 

 upper end of the stalk, and only in exceptional cases is directly 



* J. S. Miller, "A Natural History of the Crinoiiea or Lily-shaped Animals," 

 Bristol, 1821. J. V. Thompson, " Sur le Pentacrirms Europaeus, 1'etat de 

 jeunesse du genre Comatula," L'institut, 1835. J. Miiller, " Ueber den Bau 

 von Pentacrinus caput Medusae," Alliandl. dcr Bert. Aliad., 1841. J. Muller, 

 "Uebcr die Gattung Cornatula mid ihre Arten," Al/handl. dcr Bcrl. Al'ad., 

 1847. Loop. v. P.ueh, " Ueber Cystideen," AWtandl. dcr Bcrl. Aliad., 1844. 

 Ferd. Homer. " Monographic der i'ossilen Crinoideen farnilie der Blastoideen," 



