CONTENTS 



PAGE 



Introduction 1 



Chapter I. — The Germ Cells 7 



The Ovum 7 



Ovulation and Menstruation 10 



The Spermatozoon 10 



Mitosis and Amitosis 12 



Maturation 14 



Fertilization 19 



Heredity and the Determination of Sex 21 



Chapter II. — Cleavage and Formation oe the Germ Layers 23 



Cleavage in Amphioxus, Amphibia, Birds, and Reptiles 23 



Cleavage in Mammals 26 



Origin of the Ectoderm and Entoderm 28 



Origin of the Mesoderm, Notochord and Neural Tube 29 



The Notochord 35 



Chapter III. — The Study oe Chick Embryos 36 



Chick Embryo of Twenty Hours 36 



Chick Embryo of Twenty-five Hours (7 Segments) 38 



Transverse Sections 40 



Chick Embryo of Thirty-eight Hours (17 segments) 43 



General Anatomy 43 



Transverse Sections 47 



Derivatives of the Germ Layers 54 



Chick Embryo of Fifty Hours (27 segments) 55 



General Anatomy 55 



Transverse Sections 59 



Chapter IV. — The Fetal Membranes and Early Human Embryos 68 



Fetal Membranes of the Pig Embryo 68 



Umbilical. Cord 70 



Early Human Embryos and Their Membranes 71 



Anatomy of a 4.2 mm. Human Embryo 79 



Age of Human Embryos 87 



Chapter V. — The Study or Pig Embryos 89 



The Anatomy of a 6 mm. Pig Embryo 89 



External Form and Internal Anatomy 89 



Transverse Sections 104 



The Anatomy of 10-12 mm. Pig Embryos 112 



External Form and Internal Anatomy 112 



Transverse Sections 125 



Chapter VI. — Methods oe Dissecting Pig Embryos: Development oe the Face, Palate, 



Tongue, Teeth and Salivary Glands 137 



Directions for Dissecting Pig Embryos 137 



Dissections of 18-35 mm. Embryos 140 



Development of the Face ] 44 



Development of the Hard Palate 146 



Development of the Tongue 149 



Development of the Salivary Glands 152 



Development of the Teeth 153 



vii 



