286 



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. CEINOIDEA.* 



Globular or cup-shaped Echinodermata with segmented arms fur- 

 nished ivith pinnulce. They are usually attached by a segmented 



calcareous stalk. The 

 skin upon the aboral 

 side is provided ivith 

 plates, the amlulacral 

 appendages have the 

 form of tentacles, and 

 are situated in the 

 ambulacral furrows of 

 the calyx and of the 

 segmented arms. 



The greater number 

 of Crinoidea are cha- 

 racterised by the pre- 

 sence of 

 stalk 



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 Comatula 

 (fig. 232) and Actino- 

 metra, this stalk is 

 only present in the 

 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 



a segmented 

 bearing cirri. 



F(O. 231. Tentacrinus capuf Medutas (after J. Muller). 

 O, mouth ; A, anus, of the disc, which is represented from 

 the oral side. 



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

 Bristol, 1821. J. V. Thompson, " Sur le Pentacrinus Europjens, 1'elat de 

 jeunesse du genre Comatula," L'institut, 1835. J. Miiller, " Uebcr den Ban 

 von Pentacrinus caput Medusas," Abhaiull. dt-r Herl. Altad., 1841. J. Miiller, 

 "Ueber die Gattnng Comatula und ihre Artcn," AlhniuU. der Ilcrl. Alttd., 

 1847. Leop. v. Buch, " Ueber Cystidcen," Aliftandl. drr Bcrl. Alntil ., 1844. 

 Ferd. Romer, " Monograj)hie der fossilcn Crinoideen familie der Blastoideen," 



