CONTENTS 



Preface . . . 

 Introduction 



Page 

 vii 



1. The Animal Kingdom i 



The Linnaean System 2 



The Animal Phyla 3 



Summary of Classification 3° 



Sequence of Organisms in Geologic Time 34 



2. Reproduction 35 



Differentiation of Sexes 35 



The Germinal Bodies 36 



Eggs of Fishes 3^ 



Eggs of Amphibians 39 



Eggs of Reptiles and Birds 39 



Eggs of Mammals 4^ 



Relative Size 42 



Fertilization 4? 



Developmental Potentialities 44 



Means of Exit 44 



Oviparity, Viviparity, Impregnation 45 



Protection, Nutrition, and Respiration during Development 46 



In Fishes 46 



In Amphibians '• 49 



In Reptiles and Birds 5i 



In Mammals ... 53 



Evolutionary Significance ... • • 55 



Development -5° 



Cleavage and Blastula 5^ 



In Amphioxus 59 



In Amphibians 60 



In Reptiles and Birds 62 



Gastrula 63 



In Amphioxus 63 



Significance of the Gastrula 64 



In Amphibians 66 



In Reptiles and Birds 69 



Comparisons 7o 



Third Layer, Mesoderm 7i 



In Amphioxus 7i 



In Amphibians 74 



In Reptiles and Birds 76 



Early Development in Placental Mammals 77 



Organogenesis ^° 



