THE FORMATION OF CENTROSOMES IN 

 ENUCLEATED EGG-FRAGMENTS.^ 



BY 



NAOHIDE YATSU. 



With 8 Figures 



I. Introduction 287 



II. Solutions and Precautions Against Accidental Fertilization 289 



III. Experiments on the Egg at the Metaphase of the First Maturation Mitosis 291 



A. Eaucleated Fragments Treated with CaClj Solution, Heat-sterilization 291 



a. Methods 291 



h. Cytasters Studied in Life 291 



c. Cytasters Studied in Sections 293 



d. Nature of the Central Granules, and Development of the Cytasters 299 



B. Enucleated Fragments Treated with CaCb Solution, Time-sterilization 301 



C. Enucleated Fragments Treated with MgC'o Solution, Heat-sterilization 301 



IV. Experiments on the Egg before the Dissolution of the Germinal Vesicle; CaCl2 Solution, 



Heat-sterilization 303 



V. Review of Literature 304 



VI. Conclusions 308 



VII. Summary 310 



VIII. Literature 311 



I. INTRODUCTION. 



Whether or not an aster containing a centrosome (centriole) 

 may arise in the egg-cytoplasm independent of preexisting centers 

 is a cytological problem of high interest. This seemingly difficult 

 question may be decided by a simple experiment. If we are able 

 to produce an aster with the centriole in an egg-fragment con- 

 taining no preexisting centrioles, we cannot escape the conclusion 

 that these structures may be formed de novo in the egg-cytoplasm.^ 



^The main part of the present paper was carried on in the summer of 1904 under a grant from the 

 Carnegie Institution, to which I wish to express my sincere thanks. To Prof. E. B. Wilson I acknowl- 

 edge my great indebtedness for his kindly advice and criticism during the progress of this work. I am 

 also under obligation to Prof. J. S. Kingsley, Director of the Harpswell Laboratory, for his kindness 

 extended to me in many ways during my stay at his laboratory. 



'The presence or absence of the centrosome, ;'. e., the larger body surrounding the central granule or 

 centriole, need not concern us here; for according to the latest work (for example, of Vejdovsky and 

 Mrazek, Meves, Bouin), the centrosome is a periodical accumulation of the special substance, centro- 

 plasm, around the centriole, which alone can be considered as a constant and autonomous structure. 



