126 THE AMPHIOXUS. 



even yet attained to its complete separation. There 

 may, indeed, be seen on the side view of the embryo, 

 the series of cells of the neural plate, passing over 

 in unbroken continuity into the lower epithelium of 

 the front end of the body. 



FORMATION OF TWO ANTERIOR ENDODEEM DIVERTICULA. 



In the stage with seven mesoblastic somites a forma- 

 tion makes its appearance in the anterior region of the 

 hypoblast of the body, that is, in front of the meso- 

 blastic somite region, whose remarkable destinies will 

 attract our special attention in the later stages. This 

 formation consists of two dorsal folds of the hypoblast. 

 These appear more or less simultaneously with the 

 formation of the notochord fold in this region, and 

 relations of their positions to the notochord fold remind 

 one of those of the mesoblast folds in the region of the 

 body (Figs. 105, 106). 



In the foregoing section of development, the com- 

 pletion of these folds becomes continually more 

 pronounced, and they form two lateral, and at first 

 symmetrical, diverticula, at the anterior end of the 

 alimentary canal. The conditions may be recognised 

 as well on the side view (Figs. 48, 50), and the 



