CONTENTS XV 



PAGE 



Further developmental processes of both types : coelomic 



sacs, gills, genital organs, nervous system, etc. . . . 384 



General considerations: relationships to the Echinodermata ; 



segmentation ; relationships to the Chordata . . . 388 



Literature 390 



Chapter XIV. Echinodermata. By E. Korschelt . . . 892 



1. Formation of the primary germ-layers, the mesenchyma, 



mouth, and anus 392 



Holothurioidea 393 



Echinoidea 398 



Asteroidea 401 



Ophiuroidea ; Crinoidea 403 



2. The origin of the enterocoele and the hydrocoele. . . 405 



Asteroidea 405 



Ophiuroidea 406 



Asteroidea (Asterina) 407 



Echinoidea ; Holothurioidea 409 



Crinoidea 411 



Divergent statements in regard to the formation of the 

 entero-hydrocoele : Ophiuroidea ; Echinoidea (two 



pairs of enterocoeles, internal segmentation) . . 413 



3. Development of the typical larval forms ; simple funda- 



mental form 415 



Crinoidea 415 



Holothurioidea : Auricularia, and direct development . 417 



Asteroidea : Bipinnaria, Brachiolaria .... 419 



Aberrant larval forms of the Asteroidea . . . 421 



Ophiuroidea : Pluteus, direct development . . . 422 



Echinoidea : Pluteus, direct development . . , 424 



4. Metamorphosis of the larva into the echinoderm . . 426 



Holothurioidea 426 



Asteroidea 432 



Ophiuroidea 437 



Echinoidea 438 



Crinoidea 443 



Regeneration and division 455 



General considerations : common features of the develop- 

 ment 456 



Radial structure of the adult forms : its derivation , . 458 

 Relationships to other divisions (value of the larval forms, 



ambulacral system) 460 



Literature 461 



