THE MATURATION AND FERTILIZATION OF 

 THE EGG OF BUFO LENTIGINOSUS. 



HELEN DEAN KING. 



CONTENTS. 



PAGE 



294 



I. Introduction 



II. Material and Method 



III. Maturation of the Ovum 297 



1. The Unripe Ovarian Egg 297 



2. Dissolution of the Germinal Vesicle and Formation of the First 



Polar Spindle 303 



The First Polar Division. 



314 



4. The Second Polar Division 318 



5. The Female Pronucleus 319 



6. Nature of the Nucleoli 320 



7. Chromatin Reduction 321 



IV. The Spermatozoon 323 



V. Fertiliz,\tion of the Ovum 325 



1. Penetration of the Spermatozoon into the Egg and the Forma- 



tion of the Astrosphere 325 



2. The Male Pronucleus 328 



3. Growth and Division of the Astrosphere 329 



4. Fusion of the Pronuclei and Formation of the Segmentation 



Spindle 330 



5. Division of the Segmentation Spindle and Formation of the 



Daughter Nuclei 333 



VI. Polyspermy 333 



VII. Summary 335 



Literature 338 



Explanation of Plates 344 



I. Introduction. 



Since the publication, in 1883, of van Beneden's classic 

 paper, " Recherches sur la maturation de I'oeuf, la fecondation, 

 et la division cellulaire," an extensive literature has appeared 



293 



