xii CONTENTS 



PAGE 



tion — Irritability — Fixed forms — Nervous system — Colo- 

 nial forms — Reproduction — Alternation of generations — 

 Summary 135 



CHAPTER IX 



ECHINODERMATA 



Characteristics — T h e starfish — Symmetry — Internal struc- 

 ture — Irritability — Mechanics of locomotion — Assimila- 

 tion — Reproduction — Regeneration — Summary 147 



CHAPTER X 



MOLLUSCA 



Shells — The living animal — Formation of the shell — The Clam 

 — Gills — Circulatory system — Alimentary canal — Nervous 

 system — Economic value — Characteristics of the group.. 154 



CHAPTER XI 



VERMES 



Irritability of the earthworm — Mechanics of locomotion — 

 Surface characteristics — Assimilation — Increase of diges- 

 tive surface — Circulatory system — A segment — Excretory 

 organs — The nervous system — Reproduction — Classifica- 

 tion — Flat worms — Round worms — Segmented worms — 

 Molluscoidea 162 



CHAPTER XII 



ARTHROPODA 



External characteristics — Nervous system — Digestive system 

 — Respiratory system — Excretory system — Circulatory 

 system — S e n s e organs — Reproduction — Appendages — 

 Classification — Crustacea — Locomotion of the lobster — 

 External characteristics — Moulting of the shell — Diges- 

 tive system — Other organs — Respiration — Reproduction — 

 Segmentation — Acerata — Myriapoda — Insecta 173 



