CONTENTS 



PAGE 



INTRODUCTION xi 



CHAPTER I 



THE FORMATION OF THE SEX-CELLS 1 



Spermatogenesis. 



" Direct " Division of the Germ-cells. 



Oogenesis. 



Comparison of Spermatogenesis with Oogenesis. 



CHAPTER II 



POLAR BODIES AND FERTILIZATION 15 



Extrusion of the First Polar Body and Egg-laying. 

 The Jelly of the Egg, and the Second Polar Body. 

 Entrance of Spermatozoon and Copulation of Pronuclei. 



CHAPTER III 



EXPERIMENTS IN CROSS-FERTILIZATION 26 



Experiments of Pfliiger and of Born on Frogs' Eggs. 

 Experiments on Other Forms. 

 Experiments of Rauber and of Boveri. 



CHAPTER IV 



CLEAVAGE OF THE EGG . .32 



Normal Cleavage. 



Correspondence of the First Cleavage-plane and the Median-plane 



of the Embryo. 



Roux's Experiments with Oil-drops. 

 Historical Account of the Cleavage of the Frog's Egg. 



vii 



