282 



ECHINODERMATA. 



The Pluteus larv?e of the OpMiirids possess long lateral arms on 



the anterior dorso- 

 ventral arch of the 

 band, on the dorso- 

 lateral edge, and 011 

 the edge of the pos- 

 terior ventral hood. 

 The Pluteus larva of 

 the Sea-urchin has no 

 lateral arms, but pro- 

 cesses are developed 

 on the edge of the 

 anterior ventral hood 

 (fig. 226). The larv* 

 of the Spatangidce are 

 characterised by an 

 unpaired apical rod, 

 and those of Echinus 

 and Echinocidaris by 

 thepresence of ciliated 

 epaulettes (fig. 227). 

 The transformation of the laterally symmetrical larva with its 



bilateral processes and com- 

 plicated organization into the 



body of the adult Echino- 



derrn is not in all cases 



effected in the same manner. 



In the Sea-urchins and Star- 

 fishes the young animal is 



developed by a process of 



new formation within the 



body of the larva, the 



stomach, intestine, and dorsal 



sac alone persisting ; while 



the transformation of the 



FIG. 226. Pluteus of a Spatangus with so-called apical rod 

 (St) (after J. Miiller). 



Auricularia into Synapta 

 takes place without the loss 

 of so many parts of the larva, 

 the young passing through a 

 pupa-like intermediate stage. 

 In the first case a 



We 



'&' 

 mass of 



FIG 227. Platen* larva of EcJiintm lirittiis with four 

 ciliated epaulettes (We) (after E. Metschuikofi) 

 from the ventral side. O, Mouth ; A, anus. 



