CONTENTS 
PAGE 
INTRODUCTION ‘ ‘ : 4 i : 1 
CHAPTER I 
Tue EvipENcE 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 
Ammocecetes 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 alimenta- 
tion—Life-history of lamprey, not « degenerate animal—Brain of Ammio- 
ceetes compared with brain of arthropod—Summary . : 4 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 F . F : 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- 
ceetes; its topographical arrangement, its structure, its origin in muco- 
cartilage—The prosomatic skeleton of Ammoccetes; the trabecule and 
parachordals, their structure, their origin in white fibrous tissue—The 
mesosomatic skeleton of Limulus compared with that of Ammoceetes ; 
similarity of position, of structure, of origin in muco-cartilage—The 
prosomatic skeleton of Limulus; the entosternite, or plastron, compared 
with the trabecule of Ammoccetes ; similarity of position, of structure, of 
origin in fibrous tissue—Summary . ; ; : : J : . 119 
