VIII EGHINODERMATA— MORPHOLOGY OF SKELETON 375 



be muddy or sandy, the base of the stem puts out lateral branches, 

 the so-called root-eiPPi, the numerous ramifications of which penetrate 

 the sea floor in all directions. The end of the stem itself may at 

 the same time branch like the root-cirri. "When the sea floor is 

 rocky, the root-cirri spread out more horizontally, accommodating 

 themselves to the surface to which they are attached, and becoming 

 cemented to it at their ends by means of a calcareous secretion. 



Further, it is almost certain that individuals of some .species, e.g. Pentacrinidon 

 and some Palfeozoic crinoids, are capable of free locomotion when tlie stem is either 

 voluntarily or accidentally 



broken. Such locomotion is -^ C 



no doubt chiefly promoted by 

 the movements of the arms, 

 the cirri serving rather for 

 attachment. 



In Holopus (Fig. 250, p. 

 305) the stem is wanting. 

 The calj'x, which resembles 

 a reversed cone in shape, is 

 cemented to the substratum 

 by means of an irregularly 

 expanded calcareous mass. 



The Anfedonidce. are 

 stalked and attached 

 only in the young stage. 

 The larval stem re- 

 sembles that of the 

 Bourgueticrinida? (Fig. 

 326) ; the cirri are 

 developed only on its 

 uppermost ossicle, on 

 Avhich five radially ar- 

 ranged cirri first appear, 

 then five interradially 

 arranged. At a certain 

 stage, differing in the 

 different species, the 

 calyx together with the uppermost columnal (i.e. the one carrying cirri), 

 which is fused Avith the infrabasals to form the eentpodopsal, separates 

 from the stem, the latter remaining attached to the place where it was 

 fixed. Above the cirri already formed, i.e. between them and the base 

 of the calyx, new whorls of cirri continuously appear on the centro- 

 dorsal, Avhich constantly increases in size, so that we are tempted to 

 consider this piece as part of the stem, consisting entirely of nodal 

 ossicles fused together without intervening internodes. 



The Comatulidae can both swim by the rowing movements of their arms, and 

 creep by means of the cirri and of the arms. They can, further, anchor themselves 

 by their cirri, the arms being then directed upwards. 



KiG. 326. —Several stalked young stages of Antedon 

 phalanglum (A) ; Antedon spec. (B) ; Antedon tuberosa (C) ; 

 anil Antedon multlspina (D), after P. H. Carpenter. For 

 lettering see p. 317. cia. Points of attachment of the cirri. 



