Vobnne XIII. May, iSgy. Number 2. 



JOURNAL 



RPHOLOGY. 



THE EARLY DEVELOPMENT OF MARINE 



ANNELIDS. 



A. D. MEAD. 



TABLE OF CONTENTS. page 



Part L — Descriptive 229 



A. Amphitrite ornata Verrill 229 



I. Cleavage to 64 Cells 231 



Summary 237 



II. Later Cleavage to Formation of Paratroch 237 



a. Anterior hemisphere 237 



b. Posterior hemisphere 240 



Completion of prototroch 240 



Somatic plate cells 240 



The bilateral divisions of the somatic plate 241 



The cleavage of the remaining ectoderm cells in the posterior 



hemisphere 245 



Entoderm 246 



Mesoderm 246 



Summary 248 



III. Formation and Elongation of the T7-U7tk 250 



Shifting of areas on the lower hemisphere 250 



Formation of metameres 254 



Alimentary tract 254 



Mesoderm 255 



