ii2 THE AMPHIOXUS. 



towards the front becomes quite flattened (Fig. 

 105). 



We can further also see in the older stages (see 112- 

 115), that the closing of the fold, the growing over 

 of the cells, and the separation of the notochord 

 foundation from the bounding of the lumen of the 

 archenteron follows in the anterior end the general 

 process, except that here the advance of the process 

 is observed from back to front. 



The complete separation of the notochord in the 

 anterior end of the body is only completed in the 

 first stage of the next period of development (Figs. 

 120-123). 



The details of this process I do not wish to describe 

 more fully. I will only point to the comparison of the 

 figures : Figs. 87, 94, 97-99, 109 correspond to each 

 other, also Figs. 93, 96, 108, 115, 123, also Figs. 86, 95, 

 107, 122, also Figs. 105-106, 113-114, 121, also Figs. 

 104, 112, 120, each in their own region of the body. 



FURTHER FORMATION OF THE MESOBLASTIC SOMITES. 



We will now proceed to the consideration of those 

 processes of development which concern the meso- 

 blastic somites. 



