I!. AMPHIOXUS AND THE ANCESTRY 

 OF THE VERTEBRATES. 



BY 



ARTHUR WILLEY, B.Sc. LOND,, 



Tutor in Biology, Columbia College ; Balfour Student of the 

 University of Cambridge. 



Ready in September. 



The purpose of this volume is to consider the problem of the 

 ancestry of the Vertebrates from the standpoint of the anat- 

 omy and development of Amphioxus and other members of the 

 group Protochordata. The work opens with an Introduction, 

 in which is given a brief historical sketch of the speculations 

 of the celebrated anatomists and embryologists, from Etienne 

 Geoft'roy St. Hilaire down to our own day, upon this problem. 

 The remainder of the first and the whole of the second chapter 

 is devoted to a detailed account of the anatomy of Amphioxus 

 as compared with that of higher Vertebrates. The third chapter 

 deals with the embryonic and larval development of Amphioxus, 

 while the fourth deals more briefly with the anatomy, embryology, 

 and relationships of the Ascidians; then the other allied forms, 

 Balanoglossus, Cephalodiscus, are described. 



The work concludes with a series of discussions touch- 

 ing the problem proposed in the Introduction, in which it is 

 attempted to define certain general principles of Evolution by 

 which the descent of the Vertebrates from Invertebrate ancestors 

 may be supposed to have taken place. 



The work contains an extensive bibliography, full notes, and 

 135 illustrations. 



TABLE OF CONTENTS. 



INTRODUCTION. 



CHAPTER I. ANATOMY OF AMPHIOXUS. 

 II. Ditto. 



III. DEVELOPMENT OF AMPHIOXUS. 



IV. THE ASCIDIANS. 



V. THE PROTOCHORDATA IN THEIR KELATION TO 

 THE PROBLEM OF VERTEBRATE DESCENT. 



