INTRODUCTION. 3 



the beginning of April till the middle of June, 

 1879, and there made a study of the development of 

 the embryo, both 011 the living material, as well as 

 with the assistance of reagents, and by sections. 

 Further, any details which were then lacking I 

 examined carefully in the course of the next year, 

 by means of a large quantity of material which I had 

 preserved. 



In the main, the results at which I have arrived 

 are merely a confirmation of Kowalevsky's discover- 

 ies ; yet, in my opinion, our knowledge of this im- 

 portant development is largely increased, owing to 

 the completeness of my investigation, the correction 

 of several erroneous details, and the bringing to light 

 of some important facts. There seems, therefore, 

 sufficient reason for publishing these investigations 

 in full. 



SURVEY OF PREVIOUS TREATMENT 

 OF THE QUESTION. 



THE knowledge which we have hitherto had regard- 

 ing the development of the Amphioxus is derived 

 chiefly from Kowalevsky's investigations. Before his 

 time we had nothing but a few essays, written some 



