CONTENTS xi 



SECTION IV 

 Cyclostomata or Marsipobranchs 



By J. Arthur Thomson, MA., Professor of Zoology in the 

 University of Aberdeen 



CHAPTER I 



PAGE 



Introductory 441 



General structural characters and definition. 



CHAPTER II 



Myxinoids or Hag-fishes . 442 



Characters. Habits. Mode of feeding. Life-history. Variability. 

 Adaptations in struggle for existence. Classification. 



CHAPTER III 



Petromyzonts or Lampreys 449 



Characters. Habits. Mode of feeding. Life-history. Classification. 

 Relationships of Cyclostomes. 



SECTION V 



By the Same 



The Lancelets. Cephalochorda 457 



General position. External appearance. General characters. Functions 

 and habits. Development and life-history. Relationships. Classi- 

 fication. Distribution. Features of special evolutionary interest. 



SECTION VI 



TUNICATES 

 By the Same 

 CHAPTER I 



Structure • 473 



General characters ; a typical solitary Tunicate. 



CHAPTER II 



Classification and Development 479 



Classification of Tunicates. Order I. Appendicularians. Order II. 

 Ascidians. Order III. Salpians. Numbers, relationships. Life- 

 history of a typical Ascidian. 



SECTION VII 



By the Same 



Hemichorda 489 



Animals included in the group ; structure and habits of Enteropneusta, 

 their development and distribution; incipient species; structure of 

 Cephalodiscus and Rhabdopleura. 



Index 495 



