xit DEVELOPMENT OF THE LANCELET $7$ 



ectoderm and endoderm is at first a space, the greatly dimi- 

 nished segmentation-cavity, which gradually becomes entirely 



FIG. 151. Stages in the segmentation of the oosperm of Amphioxus. 

 E, represents the four-celled stage (C) from above; H, vertical section of G ; K, 

 vertical section of the blastula stage (I). (From Korschelt and Heider's 

 E)}ibryolo^v, after Hatschek.) 



