CONTENTS 



PAGE 



4. Alimentary System 34 



Digestion 



Intracellular Digestion 35 



Extracellular Digestion 

 Openings into Digestive Cavity 



Fore, Mid, and Hind-Guts 37 



Digestive Cells and Glands 40 



Movements of Food in Alimentary Canal 



5. Respiratory System 



Branchiae, Gills 41 



Tracheae, Lungs 44 



6. Circulatory System 47 



Blood- Vascular System 



Circulation and Respiration 49 



7. Excretory System 54 



Nephridia 



Proto-nephridia ^^ 



Meta-nephridia 



Kidneys of Chordata ; Pronephros ^7 



Mesonephros j'S 



Metanephros ^g 



Theories of Excretion 61 



Excretory Ducts as Sex Ducts 



8. Reproductive System 62 



Sexual Reproduction; Sexes 



Ovaries and Testes 63 



Gonads of Vertebrates 64 



Semination 65 



Secondary Sexual Characters 



Asexual Reproduction, or Monogony 66 



9. Nervous System 



( 1 ) Diffuse nervous system 69 



(2) Linear nervous system 



(3) The ganglionic type 70 



vii 



