SECT, vii PHYLUM ECHINODERMATA 177 



slender stalk by which they are permanently fixed. In the 

 ordinary Feather-stars the larva passes through a stage 

 in which it is attached by means of a stalk like the stalked 

 Crinoids : after a time the stalk becomes absorbed and the 

 young Feather-star becomes free. 



A remarkable feature of the Echinodermata is the pre- 

 vailing radial arrangement of their parts, a feature in which 

 they resemble the very much more simply organised 

 Coelenterata. But underlying this there is to be detected a 

 more obscure arrangement of the body in right and left 

 halves, just as in the bilateral animals we have been more 

 recently dealing with. This bilateral symmetry is almost 

 completely disguised by the radial arrangement of most 

 of the parts. In the larva the symmetry is strongly bi- 

 lateral; and it is only by passing through a remarkable 

 metamorphosis, in which parts of the larva are sometimes 

 altogether discarded, that the radially constructed adult form 

 is developed. 



Man. Zool, 



