CONTENTS. 



PACE 



INTRODUCTION i 



I. ANATOMY OF AMPHIOXUS 7 



HISTORICAL 7 



HABITS AND DISTRIBUTION 9 



EXTERNAL FORM 12 



Cranium and Sense-organs 17 



INTERNAL ANATOMY 22 



Atrial Cavity 22 



Viscera 24 



Ccelom 26 



Structure of Pharynx 27 



Evolution of the Thymus Gland 29 



Endostyle 31 



Branchial Bars 32 



Musculature 34 



NOTES 38 



II. ANATOMY OF AMPHIOXUS 46 



INTERNAL ANATOMY (continued') 46 



Vascular System 46 



The Excretory System 55 



Development of the Atrial Cavity 75 



Comparison between the Excretory System of Amphioxus and 



that of the Annelids 78 



Nervous System 82 



NOTES ..... . 98 



xi 



