IX 



PHYLUM ECHINODERMATA 



415 



already mentioned, 

 there are no hard parts 

 of any kind. Around 

 the mouth is a whorl of 

 tentacles pinnate, 

 shield-shaped, or arbor- 

 escent. The tube-feet 

 are sometimes entirely 

 absent. When present 

 they are usually uni- 

 form in character 

 throughout, and may be 

 arranged in five regular 

 longitudinal rows, o r 

 scattered over the entire 

 surface. Sometimes, as 

 has already been stated 

 in the account of Colo- 

 chirus, the tube-feet of 

 the dorsal and even 

 some of those of the 

 ventral surface may 

 assume the form of 

 papillae. In the Elasi- 

 poda the tube-feet of 

 the dorsal surface are 

 remarkably modified, 

 taking the form of 

 greatly elongated pro- 

 cesses. 



In the Crinoidea 

 the general shape is 

 that which has been 

 described in the case of 

 the Feather-star star- 

 like, with a central disc 

 and a series of radiat- 

 ing arms, which usually 

 branch dichotomously. 

 In the stalked forms 

 (Fig. 347) a stalk, con- 

 sisting of a row of elon- 

 gated ossicles connected 

 together by bundles 

 of ligamentous fibres, 

 attaches the animal to 

 the sea-bottom. Along 



FIQ. 347. Metacrinus interruptus. 

 (After P. H. Carpenter.) 



