CONTENTS 15 



PAGE 

 CHAPTER XXII 



The Crayfish, a Crustacean Arthopod __________ 393 



Classification, 393; Habitat and Behavior of Cra\iish, 396; Ex- 

 ternal Structure, 396; Internal Structure, 400; Metabolism, 406; 

 Eeproduction, 407; Regeneration and Autotomy, 409; Economic Re- 

 lations, 410; Characterization of Other Crustacea, 410; Recapitula- 

 tion Theory or Biogenetic Law, 413; Phylogenetic Advances of 

 Arthropoda, 414. 



CHAPTER XXIII 



The Locust, a Representative of Insects (By Vasco M. Tanner) _ 415 



CHAPTER XXIV 



Animal Parasitism (By Sewell H. Hopkins; ________ 428 



Social Relations of Animals, 428; Origin of Parasitism, 429; De- 

 grees of Parasitism, 429; The Successful Parasite, 430; Means of 

 Infection and Transmission, 433; Parasitism and Host Specificity, 

 434; Parasites and the Groups in the Animal Kingdom, 435; Some 

 Representative Parasites, 440. 



CHAPTER XXV 



The Animal and Its Environment (By A. O. Weese) ______ .457 



The Principal Biotic Formations, 462; Adaptation, 465; Succes- 

 sion, 465; Animal Populations, 468; Seasonal Changes, 470; Sum- 

 mary, 471. 



CHAPTER XXVI 



Animal Distribution (By Willis Hewatt) _________ 472 



Life Regions and Zones of the Earth, 472; Migration of Animals, 

 477; Means of Dispersal and Barriers, 478; Effects of Man Upon 

 Distribution, 479. 



CHAPTER XXVII 



The Theory of Evolution ______________ 480 



Colony Formation in Certain Protozoa, 482; Development of the 

 Gastrula, 482; Trochophore Larva, 482; Peripatus and the Worm- 

 like Ancestry of Arthropoda, 483; Echinoderms and Their Larval 

 Relations, 483; Ancestry of the Vertebrates, 484; Basis for the 

 Theory of Evolution, 488. 



GLOSSARY 

 Glossary ____________________ 510 



