OBSEEVATIONS ON OOKINESIS IN CEREBBATULUS 

 LACTEUS, VEERILL/ 



NAOHIDE YATSU. 

 CONTENTS. 



PAGE 



I. Introduction 354 



II. Structure of the egg 354 



a. Cytoplasm 354 



b. Nuclear fluid 350 



c. Nucleolus and chromatin diminution 358 



III. Centriole and centrosome 3<il 



a. Centriole 301 



b. Centrosome 302 



c. History of the centriole in fertilization and in cleavage. . . . .'!i!T 



1. Sperm centriole 307 



a. Observations 307 



b. Literature and general remarks 371 



2. Cleavage centriole 373 



d. Division of the centrosome 374 



1. Observations 374 



2. Types of centrosome division 370) 



3. Cycle of centrosome 379 



IV. Rays and spindle 380 



a. Terminology 380 



b. Observations 381 



V. Cytodieresis 384 



a. Observations 384 



1. Movement of chromosomes and centres 384 • 



2. Spindle 385 



3. Centrosome 385 



^I wish to express my obligation to Professor Wilson for his advice and sug- 

 gestion during the progress of this work and the preparation of this paper, 



and to Professor Kingsley, Director of the Ilarpswell Laboratory, for his con- 

 tinued kindness during my stay at his laboratory. 



The .Toiirnal of MonnioLOCY.— Vol. XX. No. 3. 



