MATURATION PHENOMENA IN ARTIFICIAL 



PARTHENOGENESIS OF ASTERIAS 



FORBESII* 



H. W. BEAMS. 



TABLE OF CONTENTS. 



I. Introduction 1 55 



II. Material and Method 1 56 



III. Observations: 



1 . Normal maturation 156 



2. Eggs that extrude one polar body 158 



3. Eggs that extrude no polar bodies 158 



4. Monocentric mitosis j 59 



5. Some unusual types 1 60 



6. Effect of the double method of activation on the matura- 



tion phenomena 162 



V. Discussion 1 63 



VI. Conclusion 167 



VII. Bibliography 168 



VIII. Plates 170 



INTRODUCTION. 1 



Recent studies in artificial parthenogenesis of eggs that are im- 

 mature when activated has resulted in several views as to the 

 mode of maturation which may lead to normal development. Pro- 

 fessor Tharaldsen found as a result of his previous observations 

 of the maturation phenomena in Asterias forbcsii, which may be 

 artificially activated before the maturation process is completed, 

 that this process was subject to wide variations. He proposed 

 therefore that I make a study of the maturation phenomena in 

 Asterias to ascertain the cytological details of the various types. 



* Contribution from the Zoological Laboratory, Northwestern Univer- 

 sity, Evanston, 111. 



1 I wish to acknowledge my indebtedness to Professor C. E. Tharaldsen 

 for the use of his material and his kind assistance during the progress of 

 this work. I also wish to express my appreciation of the helpful suggestions 

 given by Professor A. E. Cole and Mr. G. B. Pickwell. 



155 



