EXPERIMENTAL STUDIES ON NUCLEAR AND CELL DIVISION 



IN THE EGGS OF CREPIDULA. 



By Edwin G. Conklin 



CONTENTS. 





Introduction • • && 



I. Abnormalities found in Nature 605 



IL Cleavage of Isolated Blastomeres 608 



III". Effects of Pressure on Cleavage 510 



1. Modifications of the Cleavage Pattern Ml 



2. Differential and Non-Differential Cleavages 515 



IV. Effects of Electric Current 518 



v! Effects of Abnormal Temperature 524 



526 



VI. Effects of Ether 



VII Effects of Decreased Oxygen Tension 



1. Boiled Sea Water i ?27 



527 



2. Atmosphere of Hydrogen 



530 



VIII. Effects of Carbonic Acid 



IX. Effects of Diluted Sea Water jg* 



X. Effects of Hypertonic Sea Water .. .... sao 



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



trosomal Division . • • • ;• •» « •*•• 5i» 



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



and Centrosome ; • • • •"," "A," l!i.v <un 



3. Suppression of all Forms of Division without Stopping Nuclear Growth »w 



4. Shrinkage of Plasma, Nuclei, and Mitotic Figures J" 



5. Formation of Cytasters and Polyasters £*t 



6. Origin of Cleavage Centrosomes -,- 



7. Irregularities in the Movements of Chromosomes jQg 



8. Segregation of Chromatin and Achromatin ^ 



9. Abnormal Mitosis and Amitosis ^ 



XI. Conclusions and Summary. 553 



A. Observations and Experiments 555 



B. Cleavage and Differentiation . . 557 



C. Mitosis and Amitosis . . 559 



XII. Catalogue of Experiments 576 



XIII. Literature 



XIV. Explanation of Plates 



582 



\ 



Introduction 



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



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



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



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

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

 be preceded at every stage by a definite organization, t. «., differentiation ana 

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

 zation be only one of molecules and atoms. But many, and indeed most n> or P n °- 

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



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



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



503 



