THE DEVELOPMENT OF PARAVORTEX 

 GEMELLIPARA 



(gRAFFILLA GEMELLIPARA LINTON) 



STANLEY C. BALL 



Department of Zoology, Yale University 



SIXTEEN TEXT FIGURES AND NINE PLATES 



CONTENTS 



I. Introduction 454 



1. Determination of the species 454 



2. Historical 460 



IL Biology, material and methods 462 



III. Anatomy of the adult reproductive organs 466 



IV. Development : 473 



L Growth of the egg cells and consideration of the mitochondrial 



mass 473 



2. Formation of the egg capsule and origin of the twins 481 



a. The process in Paravortex 485 



b. Description of the newly-formed capsule 487 



c. Behavior of the vitelline cells and their nuclei 488 



3. Maturation and fertilization 492 



a. Insemination 492 



b. Maturation 493 



c. Fertilization 497 



4. Cleavage 498 



a. Micromeres and macromeres 499 



b. Behavior of the mitochondrial mass 502 



c. The blastula 503 



d. Homologues of the germ layers 504 



5. Absorption of the yolk by the primary entoderm 505 



6. Ingestion of the yolk-gorged primary entoderm cells by those of 



the secondai'y entoderm 507 



7. Gastrulation and absorption of the remaining yolk by the ectoderm 507 

 a. The embryo at the close of gastrulation 509 



8. Organogenesis to the time of birth 511 



a. The eyes 511 



b. Development of the brain and larger nerve trunks 514 



c. The pharynx 517 



d. Musculature 520 



453 



