90 THE AMPHIOXUS. 



sharply concave in the stage with three mesoblastic 

 somites, first of all flattens, and at last in the stage 

 with four and five becomes convex, and thereby rises 

 far more from the base of the neural canal. 



We will observe more closely the shrinking of the 

 neural plate. This is closely connected with its 

 diminution, the latter being due to the fact that its 

 cells alter their form while changing to high and 

 sharply pointed wedge-shaped cells. This process 

 begins in the region of the first mesoblastic somite, 

 and continues in a backward direction. We see it in 

 the stages of this section of development advanced 

 just about as far backwards as the formation of 

 mesoblastic somites. 



We see in the series of sections, represented in 

 Figs. 86-92, first of all in Fig. 86, the neural plate in 

 that place where the neural canal opens outwards, 

 flat and not as yet arched over. Further back w r e 

 meet the deepened neural canal in all sections which 

 are drawn through the mesoblastic somite region 

 (Figs. 87-91). In the region behind the mesoblastic 

 somites (Fig. 92) we find again the neural plate 

 quite flat. 



We see that the processes of formation in the 



