CONTENTS 



I. EVOLUTION OF LIFE IN RELATION TO CLIMATIC AND GEO- 



LOGICAL CHANGE 



i. The need for generality in zoology, i ; 2. What do we mean by the life of an 

 animal ? 2; 3. Li ving things tend to preserve themselves, 3; 4. What do we mean by 

 awareness of life ? 5 ; 5. The influence of environment on life, 7 ; 6. What is it that 

 heredity transmits ? 8 ; 7. The increasing complexity of life, 9 ; 8. The progression 

 of life from the water to more difficult environments, 9; 9. Changes of climate and 

 geological periods — (1) Changes of level of the continents, 11; (2) Changes of 

 climate, 13; (3) Geological time, 16; (4) Classification of geological history, 18; 

 10. Summary, 21. 



II. THE GENERAL PLAN OF CHORDATE ORGANIZATION: AMPHI- 



OXUS 



1. The variety of chordate life, 23; 2. Classification of chordates, 24; 3. Amphi- 

 oxus, a generalized chordate, 24; 4. Movement of amphioxus, 26; 5. Skeletal 

 structures of amphioxus, 29; 6. Skin of amphioxus, 29; 7. Mouth and pharynx 

 and the control of feeding, 30; 8. Circulation, 33; 9. Excretory system of 

 amphioxus, 35; 10. Nervous system, 36; 11. Gonads and development of 

 amphioxus, 41; 12. Amphioxus as a generalized chordate, 46. 



III. THE ORIGIN OF CHORDATES FROM FILTER FEEDING ANIMALS 

 1. Invertebrate relatives of the chordates, 47; 2. Subphylum Hemichordata 

 (= Stomochordata), 50; 3. Class Pterobranchia, 58; 4. Subphylum Tunicata. 

 Sea squirts, 60; 5. Development of ascidians, 66; 6. Various forms of tunicate, 

 69; 7. Class Ascidiacea. 70; 8. Class Thaliacea, 70; 9. Class Larvacea, 72; 



10. The formation of the chordates, 74. 



IV. THE VERTEBRATES WITHOUT JAWS. LAMPREYS 



1. Classification, 81; 2. General features of vertebrates, 81; 3. Agnatha, 83; 

 4. Lampreys, 83; 5. Skeleton of lampreys, 85; 6. Alimentary canal of lampreys, 

 88; 7. Blood system of lampreys, 91; 8. Urinogenital system of lampreys, 93; 

 9. Nervous system of lampreys, 97; 10. The pineal eyes, 103; 1 1. Pituitary body 

 and hypophyseal sac, 106; 12. Lateral line organs of lampreys, 108; 13. Vesti- 

 bular organs of lampreys, 109; 14. Paired eyes of lampreys, no; 15. Skin photo- 

 receptors, in; 16. Habits and life-history of lampreys, 112; 17. The ammocoete 

 larva, 114; 18 Races of lampreys, a problem in systematics, 119; 19. Hag-fishes, 

 order Myxinoidea, 122; 20. Fossil Agnatha, the earliest-known vertebrates, 125. 



V. THE APPEARANCE OF JAWS. THE ORGANIZATION OF THE HEAD 

 1. The elasmobranchs : introduction, 131; 2. The swimming of fishes, 133; 

 3. Equilibrium of fishes in water; the functions of the fins, 136; 4. Skin of 

 elasmobranchs, 141; 5. The skull and branchial arches, 142; 6. The jaws, 145; 

 7. Segmentation of the vertebrate head, 148; 8. The pro-otic somites and eye- 

 muscles, 149; 9. The cranial nerves of elasmobranchs, 152; 10. Respiration, 157; 



11. The gut of elasmobranchs, 158; 12. The circulatory system, 159; 13. Urino- 

 genital system, 162; 14. Endocrine glands of elasmobranchs, 164; 15. Nervous 

 system, 167; 16. Receptor-organs of elasmobranchs, 170; 17. Autonomic nervous 

 system, 173. 



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