302 



ECHIXODERMA 



radialia to unite in a complicated plexus in the ccntrodorsal. A pfoblematical 

 ^o-ealled Jerij/ or^;jii also beu'ins in tlie eentrodorsal and extends up through 

 the avis of the tlieea to tlie oral disc. It is apparently homologous with the 

 •heart- of other echinoderms. Its upper end lies in a cell complex trom whicli 

 the reticulum of genital cords extends into the arms, su'eUmg tn the pinnuUe 

 to the gonads ^ng'". .^oSV The dorsal organ in the ccntrodorsal is enclosed m 

 the ihanibfn-J er,cJ«. a i.rolongation of the cadom which extends into stalk and 

 cirri. 



Si(b Class I ■ F.iii'riiioidcj. 



The foregoing account applies entirely to the Eucrinoidca, which may be 

 di\ided into two groups: ■ , ■ • , n 



Order I TESSELLATA vTahrocrinoideaV Theca wiih its side walls 

 composed of immovably united thin plates; the ambulacral -rooves usually 

 completely covered bv calcareous plates. Exclusively paleozoic. 



Ftr, roy. Fio. ;oS. 



Fig. 207. — ("(ral area of crinoid {Aiih\livi). sho"iiig by dotted lines the course of the 

 intestine from the mouth [jn) to the anus [ay. ,c. ciliated grooves leading from the arms 

 to the mouth (orig.l. 



Fie.. r()S. — Cross-section of iiinnula of AiiIl\!oii Rafter FudwigV j, axial ner\e 

 cord; (", eiliateil cups; ee, cadiae canal; l;. gonad; ,n\ saeculi; .vc. subtentaeular eanal; .', 

 tentacles. 



Order IT. ARTICUL.\T.\ (XcocrlnoideaV .Vifbtilaeral grooves open, 

 theca with compact, in jiart movably articulated, plates. This order left lhe» 

 other in the nieso;^oie age, and some families have persisted until now. Rliizo- 

 criiius'-'' (fig. 2Q(i) and Pciilacriiiiis (fig. eo-|V dee]i seas; the CoiiATULlii-V; of 

 shallow water are hxed in the young, free in the adult. Anicdon* (tig. 295) 



Sub Class II. lulrioaslcroidca (Agclacrinoidca). 



Theca of irregular ]ilales; arms tinbranched and lying on the theca. Possibly 

 the ancestors of the noncrinoid echinoderms. I'aleo/.oic. Ai^cUicriitiis. 



