XIV CONTENTS 



Y. Hirudinea 3^8 



Oviposition (cocoons) 318 



1. Cleavage ; formation of the germ-layers and estab- 



lishment of the external form of the body 



(Ehyncobdellid*) 319 



Formation of the germ band 321 



Development of the embryo 323 



Gnathobdellidae : cleavage ; germ bands . . 325 



2. LarvcB of the Gnathobdellidse (ciliation and primi- 



tive kidneys) 327 



3. The further development of the body ; establish- 



ment of head and trunk 329 



4. Formation of the organs 331 



General considerations on the development and 



interpretation of the Hirudinea . . . 386 



VI. Branchiobdella 336 



Systematic position 336 



Oviposition ; cleavage ; formation of the germ- 

 layers, etc 337 



General considerations regarding Annelida : larval 



forms (Trochophore) 341 



Trochosphsera, Pilidium, and other larvae : descent . 842 



Head and trunk ; segmentation 346 



Literature 350 



Chapter XI. Sri'UNCULiD^. By E. Korschelt .... 357 



1. The development of Sipunculus (blastula, formation of 



the germ-layers) 357 



Development of the embryo 358 



The larva of Sipunculus 361 



Metamorphosis into the adult animal .... 368 



2. The development of Phascolosoma 364 



General considerations : Sipunculidse and Echiuridse as 



Gephyreans ; relationships to the Annelida . . 365 



Literature 366 



Chapter XII. Ch/etognatha. By K. Heider .... 367 

 Systematic position ; oviposition ; cleavage; formation of the 



germ-layers 367 



Further development 370 



General considerations : relationships to the Annelida ; 



absence of the larva ; coelomic sacs 871 



Literature 371 



Chapter XIII. Enteropneusta. By E. Korschelt . . . 378 



Anatomy 378 



Development without Tornaria larva: cleavage; formation of 



the germ-layers; development of the embryo; larva . . 879 



Development by means of the Tornaria 381 



