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 Palæontology-- Reasons for choosing Ammocoetes rather than Amphioxus for the investigation of this problem--Importance of larval forms-- Comparison of the vertebrate and arthropod central nervous systems--Antagonism between cephalization and alimentation-- Life-history of lamprey, not a degenerate animal--Brain of Ammocoetes compared with brain of arthropod--Summary 8