CONTENTS 



EMBRYOLOGY: PROBLEMS AND SCOPE 1 



The general nature of development, 2 

 The probems of development, 5 



OVULATION: ITS CONTROL BY HORMONES AND LIGHT 13 



Origin of the germ cells, 1 3 



Growth of the egg in the ovary, 14 



Release of eggs, 15 



Release of eggs by pituitary gland, 1 7 



The effect of light on breeding habits, 1 8 



Internal control of pituitary secretion, 20 



Human pregnancy tests, 23 



THE UNFERTILIZED EGG AND ITS ORGANIZATION FOR 



DEVELOPMENT 25 



Organization of the sea urchin egg, 27 

 Experimental study of the sea urchin egg, 29 

 The labile nature of organization, 32 

 Twinning and duplication of structures, 36 

 Theories regarding organization, 39 



FERTILIZATION: THE NATURE OF THE STIMULUS FOR 



DEVELOPMENT 43 



Sperm and egg gamones, 44 

 Morphological changes at fertilization, 47 

 Physiological changes at fertilization, 47 

 Artificial parthenogenesis, 48 

 A theory of fertilization, 49 

 Viability of eggs and sperm, 51 

 General principles, 53 



THE EARLY GASTRULA WITH ITS PRESUMPTIVE VALUES 55 



Organization in the amphibian egg, 56 



