THE DEVELOPMENT OF THEKIDIUM, AN AEANEAD, UP 

 TO THE STAGE OF REVERSION. 



THOS. II. MONTGOMERY, Jr. 



With Eight Plates. 



CONTENTS. 



PAGE 



Introduction and :Methods 298 



I. Ob.servations 299 



1. The Cleavage up to Gastrulation 299 



2. The Earlier Part of the Gastrulation 302 



3. The Later Part of the Gastrulation 303 



4. Stage of the Protozonites 308 



5. Stage of 1 to 2 Abdominal Segments 310 



6. Stage of 3 to 5 Abdominal Segments 311 



7. Stage of the Early Abdominal Appendages 312 



8. Stages Immediately Preceding Reversion 310 



9. The Stage of Reversion 320 



10. The Germ Cells ■ 32.5 



II. Summary of Observations with Comparison of the Literature 326 



11. Cleavage up to Gastrulation 326 



12. Gastrulation and Formation of the Germ Layers 328 



13. Segmentation and Appendages of the Cephalothorax 3.32 



14. Segmentation and Appendages of the Abdomen 336 



15. GroAvth Differences of Cephalothorax and Abdomen ,339 



10. Central Nervous System 340 



17. Blood Cells and Heart 342 



18. The Germ Cells 344 



19. Movement of Parts during Differentiation 344 



Literature List 349 



Explanation of Plates I-VIII 3.51 



The JouiiXAL of Moiti-iioLooy. — Vol. XX, No. 2. 



