CONTENTS xi 



PAGE 



special cells — Reproductive cells of the sea-urchin — At- 

 traction of the sexual cells — Division of the fertilized egg 

 — Differentiation of cells — The process universal — Pro- 

 tection of the cells in land animals — Sexual reproduction 

 of plants — Summary 87 



CHAPTER VI 



IRRITABILITY 



Protoplasmic motion — Ciliary motion — Muscular contraction 

 — Theory of muscular contraction — Stimuli — Rhythmical 

 contraction — Influence of the structure of muscles — In- 

 fluence of arrangement of muscles — The function of a 

 skeleton — The skeleton external in lower animals — In- 

 ternal in higher animals — The structure of bones — The 

 spinal column — The shoulder girdle — The pelvic girdle — 

 The ribs — Appendages — Joints — Relation of muscles to 

 bones — Relation of nerves to muscles — Structure of the 

 nervous system — The work of nerves — The value of the 

 nerves — Sense organs — Sympathetic system — Exercise — 

 Effect of alcohol on the nervous system — Summary 99 



PART II 



INTRODUCTION 



CHAPTER VII 



PROTOZOA 



Habitat — The ameba — More highly specialized forms — Food 

 substances — Wastes — Respiration — Reproduction — S u m - 

 mary 128 



CHAPTER VIII 



CCELENTERATA 



Many-celled animals — The primary layers — Tissues of the 

 ccelenterata — Distinguishing characteristics — Assimila- 



