CONTENTS Xlll 



PAGE 



1. Development through free-swimming larvse (Poly- 



chsbta and Archiannelida) 262 



Oviposition ; brooding 262 



Embryonic development (cleavage, blastula) . 263 



Formation of the germ-layei's ; mesoderm . . 265 



Trochophore [larva] ...... 266 



Metamorphosis of the Trochophore larva into the 



worm ......... 268 



The various larval forms (atrocha, monotrocha, 

 telotrocha, etc.), with remarks on their meta- 

 morphoses 270 



Suppression of the larval form through brooding 280 



2. Development without free-swimming larvse (Oli- 



gochseta) 281 



Oviposition (cocoons) ; cleavage .... 281 

 Formation of the germ-layers (mesodermal 



bands) 282 



The embryos in the larval condition (head kid- 

 ney) 283 



Formation of the worm 284 



Primitive segments ; formation of the mesoderm 285 



3. Formation of the organs 286 



Ectodermal structures : epidermis ; setigerous 



sacs ; nervous system and sensory organs . 287 

 Mesodermal structures : body cavity ; muscula- 

 ture ; blood-vessels 289 



Head kidney and segmental organs . . . 295 



Genital organs 297 



Entodermal structures : intestinal canal . . 299 

 Non-sexual reproduction ; regeneration ; divi- 

 sion (Lumbriculus, Ctenodrilus) . . . 801 

 " Budding " of the Naididse, Autolytus, Syllidse, 



Nereis 302 



Stock-formation of Syllis ramosa .... 304 



II. Echiuridae 304 



1. Oviposition; cleavage and formation of the germ- 



layers 304 



2. Larval form and metamorphosis of Echiurus and 



Thalassema 306 



3. Larval form and metamorphosis of Bonellia . . 310 



Development of the male of Bonellia ; general 



considerations 312 



IIL Dinophilus 313 



Resemblance to polytrochal Annelid larvae . . 313 



Oviposition ; development ; sexual dimorphism . 314 



IV. Myzostoma 315 



Embryonic development and larval form . . , 315 



Resemblance to Annelid larva? ; metamorphosis . . 316 



