INTRODUCTION. 9 



general portion, forming the conclusion of this work. 

 The history of the development of the Amphioxus will 

 be divided into two parts ; namely, the development 

 of the embryo and that of the larva. Under the 

 former will be included all those stages in which, 

 though the animal may have left its egg-membrane 

 and swims about freely by means of cilia, it is 

 still developed at the expense of the material stored 

 up in the egg. 



The processes of the development of the embryo take 

 place in forty-eight hours, and thus differ owing to 

 their speed from those of the development of the 

 larva, which occupy months. 



