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 



