THE RELATION OF THE NUCLEOLUS TO THE CHROMOSOMES IN 

 THE PRIMARY OOCYTE OF ASTERIAS FORBESII. 1 



BY H. E. JORDAN. 



INTRODUCTION. 



The following investigation was undertaken at the suggestion of Prof. 

 E. B. Wilson, to whom I am very greatly indebted for help during the 

 progress of the work. Its primary object is to contribute to the subject 

 of the relation between nucleolus and chromosomes during maturation. 

 Hartman (1902) and Guenther (1903) maintain that in certain echinoderms 

 the chromosomes of the first maturation spindle are derived from the nucleo- 

 lus. If this view is correct for all of the forms, the oocyte development in 

 favorable cases ought to reveal the entrance of the chromosomes into the 

 nucleolus. Accordingly, I have attempted to trace the history of both chro- 

 mosomes and nucleolus from the last series of oogonia through the growth- 

 period and maturation process of the oocyte of a species of starfish, Asterias 

 forbesii. My results show conclusively that in this echinoderm form, at 

 least, the chromosomes do not arise out of the nucleolus at maturation. 

 The nearest approach to such a state of affairs is where a close superficial 

 attachment gives the appearance of a nucleolar origin. Incidentally are 

 involved the questions of the function of the nucleolus, the significance of the 

 nucleolar vacuoles, and a consideration of the mechanism of maturation. 

 Observations were made on the living material and some study was devoted 

 to preserved material during a two months' stay at the U. S. Fish Commis- 

 sion station at Woods Hole in the summer of 1906. I wish here to acknowl- 

 edge many courtesies extended to me by the director, Dr. F. B. Sumner, 

 and I desire also to express my appreciation of the splendid facilities for 

 research offered by the laboratory. Further study was given to the pre- 

 served material in the Histological Laboratory of Princeton University dur- 

 ing the winter of 1906-07, under the direction and with the kindly help of 

 Prof. Ulric Dahlgren. 



Through the kindness of the Carnegie Institution of Washington I have 

 been enabled to extend the investigation to a comparative study with Hip- 



1 Thesis presented to the faculty of Princeton University in partial fulfillment of 

 the requirements for the degree of Doctor of Philosophy. 



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