DEVELOPMENT. 



139 



bscomes the epithelial covering of the tentacles which at first 

 project into the atrial cavity. When the adult condition is 



FIG. 93. Synapta larva, showing the break up of the ciliary band of the auricularia. 

 a anus ; ed prootodaeum ; ent euterocoel ; kr calcareous wheels ; m oral funnel or atrium ; 

 mg stomach ; n nerve bands ; 10 water-vascular ring with prolongations (from Korschelt 

 and Heider). 



attained the ciliated bands disappear, the oral vestibule opens 

 out and the tentacles project. 



The pluteus larva. In the Ophiuroidea and Echinoidea the 

 larva resembles the auricularia in possessing a single ciliated 

 band, but differs from it by the long arm-like processes of the 



FIG. 94. Diagrammatic figures showing the evolution of an ophiuroid pluteus from a 

 simple Echinoderm larva (from Balfour, after J. Miiller). The calcareous skeleton is not 

 represented, m mouth ; an anus ; d antero-lateral arms ; d' the long postero-lateral 

 arms ; ' postoral arms ; g' postero-dorsal arms. 



margin of the body on to which the ciliated band is continued, 

 by the small size of the preoral lobe (frontal area) and by the 



