EXPERIMENTAL STUDIES ON NUCLEAR AND CELL DIVISION 

 IN THE EGGS OF CREPIDULA. 



By Edwin G. Conklin. 



CONTENTS. 



Intboduction 503 



I. Abnobmalitibs found in Natube 505 



II. Cleavage of Isolated Blastomeees 508 



III. Effects of Pressuee on Cleavage 510 



1. Modifications of the Cleavage Pattern ' 511 



2. Differential and Non-Differential Cleavages ! ! 515 



IV. Effects of Electeic Current 518 



V. Effects of Abnormal Temperature .524 



VI. Effects of Etheb 526 



VII. Effects of Deceeased Oxygen Tension 527 



1. Boiled Sea Water 527 



2. Atmosphere of Hydrogen 528 



VIII. Effects of Cabbonic Acid 530 



IX. Effects of Diluted Sea Watee 532 



X. Effects of Hypeetonic Sea Watee 536 



1. Suppression of Yolk Division, without Suppression of Protoplasmic, Nuclear or Cen- 



trosomal Division 538 



2. Suppression of Division in both Yolk and Protoplasm, without its Suppression in Nucleus 



and Centrosome 539 



3. Suppression of all Forms of Division without Stopping Nuclear Growth 540 



4. Shrinkage of Plasma, Nuclei, and Mitotic Figures 541 



5. Formation of Cytasters and Polyasters 542 



6. Origin of Cleavage Centrosomes 544 



7. Irregularities in the Movements of Chromosomes 547 



8. Segregation of Chromatin and Achromatin 548 



9. Abnormal Mitosis and Amitosis 550 



XI. Conclusions and Summaby 553 



A. Observations and Experiments 553 



B. Cleavage and Differentiation 555 



C. Mitosis and Amitosis 557 



XII. Catalogue of Expeeiments 559 



XIII. LlTEBATUEE 576 



XIV. Explanation of Plates 582 



Introduction. 

 Many problems of development, heredity and evolution center in the study 

 of the causes and nature of differentiation, and particularly of the early differ- 

 entiations of the egg. Some of these differentiations have been traced back to 

 very early stages of development without finding their real beginnings, and 

 indeed it is clear that a definite sequence of morphological differentiations must 

 be preceded at every stage by a definite organization, i. e., differentiation and 

 integration, of the developing substance, even though this antecedent organi- 

 zation be only one of molecules and atoms. But many, and indeed most morpho- 

 logical differentiations arise in the course of development by a process of epigen- 

 esis, or creative synthesis, from other differentiations more or less unlike in kind. 

 The great problem of development is to determine, as far as may be possible, 



503 



