286 



ECHINODEKMATA. 



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.* 



Globidar or cup-shaped Echinodermata with segmented arms fur- 

 nished with pinnulw. 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 

 T'ryf ambulacral furroios of 



' -i/^ "J ^ te ca ^J x ana f the 

 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 Comatula 

 (fig. 232) and Actino- 



FIG. ZSl.Pentacrimu capiit Medtinai (after J. Miiller). metra > "US Stalk is 

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

 the oral side. r m , , . 



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 Crinoidea or Lily-shaped Animals," 

 Bristol, 1821. J. V. Thompson, " Sur le Pentacrinus Europseus, Petat de 

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

 von Pentacriuus caput Medusas," AbJuutdl. drr fieri. Akad., 1841. J. Miiller, 

 "Ueber die Gattnng Comatula mid ihre Arten," Alliainll. drr fieri. AJtad.\ 

 1847. Leop. v. Much, "Ueber Cystideen," Abhandl. drr fieri. AA-ad., 1S44. 

 Ferd. Eomer. " Monographic der fossilen Crinoideeu familie dor Blastoidecn," 



