THE EARLY DEVELOPMENT OF AMPHIOXUS. 589 



The Early Development of Amphioxus. 



By 



E. W. MacBride, M.A., 



Fellow of St. John's College, Cambridge ; Professor of Zoology in the McGill 



University, Montreal. 



With Plates 43—45. 



The work which forms the subject of the present essay was 

 carried out in the Cambridge Zoological Laboratory during 

 the years 1895-7. The material on which ray results are 

 founded consisted of a collection of embryos and larvae which 

 had been obtained by Mr. Sedgwick and Dr. Willey during 

 their visits to Faro in 1890-91, and I have to express my 

 warmest thanks to Mr. Sedgwick for placing this valuable 

 material at my disposal. 



It will, no doubt, be the opinion of many zoologists that a 

 fresh paper on the early development of Amphioxus needs 

 considerable justification, since it may appear superfluous to 

 attempt to improve on the admirably clear account given by 

 Hatschek (3 and 5) of this subject, an account which has be- 

 come incorporated in all text-books, and forms part of the 

 classical literature of zoology. That such an opinion, how- 

 ever, would not be well founded, and that on the contrary a 

 large number of doubtful points of great theoretical im- 

 portance remained to be cleared up, will be evident when we 

 briefly examine the present state of our knowledge on this 

 subject. 



The foundation of our knowledge of the development of 

 Amphioxus was laid by Kowalevsky, whose two papers (6 and 



