EFFECTS OF CENTRIFUGAL FORCE ON THE STRUC- 

 TURE AND DEVELOPMENT OF THE EGGS 

 OF CREPIDULA 



EDWIN G. CONKLIN 



Princeton University 



ONE HUNDRED AND TWENTY-FOUR FIGURES 



CONTENTS 



1. Introduction 312 



1. Historical 312 



2. General aims and results 314 



3. Material and methods 316 



II. Results of centrifuging during maturation and fertilization stages 317 



1. Before and during the first maturation division 317 



2. During the second maturation division 321 



3. Formation of giant polar bodies 322 



4. Why polar bodies do not develop 325 



5. Cleavage of eggs centrifuged during maturation stages 330 



6. The maturation pole does not determine the animal pole of the egg 



nor the ectodermal pole of the embryo 332 



7. Results of centrifuging after maturation and before the first 



cleavage 333 



III . Results of centrifuging during cleavage stages 335 



1. Modifications of first and second cleavages: Equatorial cleavages. 335 



2. Results of centrifuging during resting stages between first and 



second and second and third cleavages 337 



3. Later cleavages of eggs centrifuged in the two or four cell stages. 339 



4. Results of centrifuging during the third and fourth cleavages. . . . 340 



5. The potency of substances, regions and blastomeres of centrifuged 



eggs 343 



IV. General conclusions 346 



1. The nature and causes of cell polarity 346 



2. The structure of protoplasm 356 



3. Protoplasmic flowing and intracellular movements 362 



4. The orientations of development 364 



V. Summary and index 367 



VI. Literature cited 372 



311 



