xviii CONTENTS 



Page 



CHAPTER XLVI 



Class Arachnida "'"^ 



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

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

 Mites — Other arachnids. 



CHAPTER XLVII 



Arthropods in General "1" 



Characteristics and advances — Classification — Behavior. 



CHAPTER XLVIII 



Phylum Chordata 312 



Characteristics — Advances shown by the chordates — Classification. 



CHAPTER XLIX 



Lower Chordates 315 



Hemichordata — Urochordata — Cephalochordata — Economic value. 



CHAPTER L 



SuBPHTLUM Vertebrata 322 



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 341 



Classification — Myxinoids — Lampreys — Relationship of the cyclostomes — 

 Economic importance. 



CHAPTER LII 



Class Elasmobranchii 344 



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

 Economic facts. 



CHAPTER LIII 



Class Pisces 350 



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 365 



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

 terrestrial adaptations. 



CHAPTER LV 



Class Amphibia 370 



Classification — Urodela — Salientia — Apoda — Food — Color changes in 

 amphibia — Nervous system and sense organs — Behavior — Reproduction 

 and development — Neoteny and pedogenesis — Regeneration — Hibernation 

 — Economic importance. 



