CONTENTS. 



INTRODUCTION 



I. ANATOMY OF AMPHIOXUS , 

 Historical 



Evolution of the Thymus Gland 



PAGE 



I 



7 



7 



Habits and Distribution 9 



External Form 12 



Cranium and Sense-organs 



Internal Anatomy 



Atrial Cavity 



Viscera 



17 



22 



22 



24 



Crelom 26 



Structure of Pharynx 27 



29 



Endostyle :^I 



Branchial Bars 32 



Musculature 



34 



Notes 38 



II. ANATOMY OF AMPHIOXUS 46 



Internal Anatomy {contimicd) 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 yS 



Nervous System 82 



Notes .-..,- 98 



