6i4 



ECHINODERMATA 



podia become later enclosed in grooves in the corona, and are 

 reduced to vestiges in the adult. 



The Auricularia is the only type of Dipleurula in which 

 larval mouth and anus are retained. For this reason it has been 



antero-lateral 

 arm. 

 orjl. 



postero-dorsal 

 arm. ■. 



Fig. 291. — Pour views of Echinopluteus from the left side, to show the metamorphosis. 

 A, B, and C are taken from the development of Mchinus miliaris. D is a young 

 Echinus esculentus. The rudiment of the oral disc of the £chi7ius is seen 

 beginning in B and larger in C. ad.stom, Adult stomodaeum ; cil.ad, adoral ciliated 

 hand ; cil.ep, ciliated epaulette ; coe, coelom ; d.sp, prismatic spine of dorsal surface 

 (periproct) of adult ; ech, rudiment of Echinus ; int, intestine ; l.oes, larval oeso- 

 phagus ; mp, madreporic pore ; nerve circ, nerve - ring of adult ; pod, iirst paired 

 tuhe - feet ; st, stomach ; t, terminal tentacle of the radial hand ; v.sp, pointed 

 ventral spine of adult. A, B, and D magnified 45 diameters ; C, 60 diameters. 



supposed that its median plane of symmetry remains the median 

 plane of the adult. The researches of Bury ^ have shown that 

 this is not so. As in other types of Dipleurula (with the 

 possible exception of the Ophiopluteus) the adult position of the 



' "The Metamorphosis of Echinoderms," Quart. Journ. Micr. jJc. xxxviii. 1895, 

 p. 45. 



