"C" or Ophiura the hydroooele is a horseshoe shaped 

 structure lying in the posterior ventral part of 

 the larvae with the open end directed anteriorly, 

 and in each coo; the piano or radial symmetry of the 

 hydroc I Ls at right angles to the plane of bilat- 

 eral symmetry of the larvae. 



g In the formation of the paired tentacles from 

 the radial water canals the processis ce,~uri re-entrip- 

 eta33^y in both larvae, the second pair of tent* - 

 appearing between the first pair and the water ring, 

 instead of between ah: first pair an It. and ten- 

 tacle as is the case in the other groups of =chin- 

 oderms. - 



In the five lay Antedon larva and those st 

 represented by "D" to "F" in Ophiura, the stalk and 

 larval organ are strikingly similar both in chap a 

 n ;ition, the tv:o structures being rly 

 directed in swimming. 



The stem of the Antedon larva, as a result of 

 metamorphosis, cmoes tc be an aboral structure and 

 just before the disappearenee of the larval organ 

 from the Ophiura larva, it is to be foun;! a.s a small 



