CONTENTS 



PACK 



Introduction ^i 



CHAPTER I 



The Formation of the Sex-cells 1 



Sperinatogenesis. 



" Direct " Division of the Germ-cells. 



Oogenesis. 



Comparison of Spermatogenesis with Oogenesis. 



CHAPTER n 



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 m 



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 



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