Xiv CONTENTS 



Page 



CHAPTER XLV 



Class Insecta • 271 



External characteristics — Internal structures — Senses of insects — Reproduc- 

 tion — Autotomy — Benefits from insects — Injurious types — Combating in- 

 jurious insects — Beneficial insects — Social insects. 



CHAPTER XLVI 



Class Arachnida 296 



External structure of spiders — Internal structures — Metabolism — Reproduc- 

 tion — Spinning activities — Behavior — Economic importance — Scorpions — 

 Mites — Other arachnids. 



CHAPTER XLVII 



Arthropods in General 304 



Characteristics and advances — Classification — Behavior. 



CHAPTER XLVIII 



Phylum Chordata 306 



Characteristics — Advances shown by the chordates — Classification. 



CHAPTER XLIX 



Lower Chordates 309 



Hemichordata — Urochordata — Cephalochordata — Economic value. 



CHAPTER L 



Subphylum Vertebrata 316 



Distinguishing characteristics — Body plan — Skin — Skeleton — Muscular sys- 

 tem — Digestive system — Respiratory system — Circulatory system — Excre- 

 tory system — Nervous system — Sense organs — Ear — Eye — Reproductive 

 system — Advances shown by vertebrates — Classification. 



CHAPTER LI 



Class Cyclostomata 335 



Classification — Myxinoids — Lampreys — Relationship of the cyclostomes — 

 Economic importance. 



CHAPTER LII 



Class Elasmobranchii 338 



Dogfish sharks — Other sharks — Skates and rays — Extinct elasmobranchs — 

 Economic facts. 



CHAPTER LIII 



Class Pisces 344 



Classification — Crossopterygii — Chondrostei — Holostei — Teleostei — Dipnoi 

 — Body form — Scales — Fins — Locomotion — Air bladder — Forms of tails — 

 Colors of fishes — Internal anatomy — Food of fishes — Respiration — Senses 

 of fish — Behavior — Reproduction — Ages of fish — Deep-sea fishes — Remark- 

 able fishes — Economic relations. 



CHAPTER LIV 



Terrestrial Vertebrates 359 



Changes incident to the acquirement of a terrestrial mode of life — Origin of 

 terrestrial adaptations. 



