THE GERM-CELLS OF GKANTIA COMPRESSA. 261 



The Germ-Cells, Fertilization, and Early Development of Grantia (St/con) 

 compressa*. By J. Bronte G-atenby", B.A., B.Sc, D.Phil., Senior 

 Demy, Magdalen College, Oxford ; Senior Assistant in Zoology, Lecturer 

 in Cytology, University College, London. (Communicated by Prof. E. S. 

 Goodrich, F.R.S., Sec.L.S.) 



(Plates 19-23; and 4 Text-figures.) 

 [Read 11th December, 1919.] 



Contents. 



Page 



1. Introductory . 262 



2. General Statement of the Problems investigated 262 



3. Previous Work 263 



4. Material and Methods 264 



5. General Account of the Development of a Sycon, up to the Formation of the 



Free-swimming Amphiblastula Larva 265 



6. The Structure of the Amphiblastula Larva 266 



7. The Minute Cytology of the Gastral Epithelial or Collar Cell of Grantia .... 268 



8. Amoeboid Cell-elements of Grantia 269 



9. The Question of the Origin of the Germ-cells 270 



10. How Collar-cells become Amoeboid Cells of the Mesoglea 270 



11. Formation of Oogonia in situ from Collar-cells 271 



12. Position of Germ-cells in Grantia compressa 271 



13. Spermatogenesis in Grantia compressa 272 



14. General Description of the luclusions of the Cytoplasm in Oogenesis 273 



15. Ectoplasmic and Endoplasmic Regions in the Egg 274 



16. The Problem of the Polarity of the Oocyte, the Ovum, and the Embryo .... 275 



17. Preliminary Outline of Events leading to the Union of Sperm and Egg .... 276 



18. Evidence as to the True Identity of the Sperm-carrying Cell 277 



19. Behaviour of Sperm after Entry into Collar-cell 277 



20. Changes in the Collar-cell brought about by the Entry of the Spermatozoon. 279 



21. The Fate of the Sperm-carrying Cell after the Sperm passes into the Oocyte. 279 



22. Behaviour of Sperm and Sperm-beariug Cell explicable as a Chemotactic 



Phenomenon 280 _ in «, 



23. The Entry of the Spermatozoon into the Egg and the Effect on both Gametes. 280 j AN J 



24. The Fate of the Middle-piece or Sperm Macromitosome ("X benkern ") during 



Fertilization 281 V "^ J 



25. The Mitochondria in the Development of Grantia com2)ressa 281 



26. Differentiation of the Nuclei of the Blastula-wall heralding the Formation of 



Two Definite Tissues , . . . 282 



* [The materials and part of the reagents used in this research were purchased by a 

 Government Research Grant of the Royal Society, for which I express 'my grateful 

 thanks.] 



LINN. JOURN. ZOOLOGY, VOL. XXXIV. 20 



