CONTENTS 



PAGE 



Introduction 1 



CHAPTER I 

 The Evidence of the Central Nervous System 



Theories of the origin of vertebrates — Importance of the central nervous system 

 — Evolution of tissues — Evidence of Paleontology — Reasons for choosing 

 Ammoccetes rather than Amphiosus for the investigation of this problem — 

 Importance of larval forms — Comparison of the vertebrate and arthropod 

 central nervous systems — Antagonism between cephalization and alimenta- 

 tion — Life-history of lamprey, not a degenerate animal — Brain of Ammo- 

 ccetes compared with brain of arthropod — Summary . . ■ . . 8 



CHAPTER II 



The Evidence of the Organs of Vision 



Different kinds of eye — Simple and compound retinas — Upright and inverted 

 retinas — Median eyes — Median or pineal eyes of Ammoccetes and their 

 optic ganglia — Comparison with other median eyes — Lateral eyes of verte- 

 brates compared with lateral eyes of crustaceans — Peculiarities of the 

 lateral eye of the lamprey — Meaning of the optic diverticula — Evolution 

 of vertebrate eyes — Summary 68 



CHAPTER III 



The Evidence of the Skeleton 



The bony and cartilaginous skeleton considered, not the notochord — Nature of 

 the earliest cartilaginous skeleton — The mesosomatic skeleton of Ammo- 

 ccetes ; its topographical arrangement, its structure, its origin in muco- 

 cartilage — The prosomatic skeleton of Ammoccetes ; the trabeculse and 

 parachordals, their structure, their origin in white fibrous tissue — The 

 mesosomatic skeleton of Limulus compared with that of Ammoccetes ; 

 similarity of position, of structure, of origin in muco-cartilage — The 

 prosomatic skeleton of Limulus ; the entosternite, or plastron, compared 

 with the trabeculse of Arnmocoetes ; similarity of position, of structure, of 

 origin in fibrous tissue — Summary 119 



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