422 



ZOOLOGY 



SECT 



modified by the formation, except in the Crinoidea, of variously 

 arranged processes along its course. The resulting larva, echino- 

 pcedium or dipleurula, always exhibits marked bilateral symmetry. 

 It has a pre-oral lobe on which an apical plate comparable to that 

 of the trochophore (p. 316) may be developed. 



FlQ. 348. Diagram,-} of the development of the larva) of Echinoderms., 1, Primitive form 

 of Echinoderm larva ; 2 and:}, Development of an auricularia (Holothuroidea) ; 4, f>, and , 

 Development of a hiphinaria ( Asteroidea) ; 7, 8, and 9, Development of a plutewt (Echi- 

 noidea and Ophinroidea). aor. in 1 and 7, adoral band of cilia, in 4, 5 and . pro-oral loop ; 

 uli. alimentary ranal ; an. anus ; b, b. processes or arms ; mo. mouth ; por. in J, 2, 7 and i>, 

 peri-oral ciliated band and processes, in 3, 4, 5 and (>, itust-oral loop. (From Leuckart and 

 Nitsche's Diagrams.) 



