84 THE AMPHIOXUS. 



acid, as well as by a stronger carmiii staining of the 

 mesoblastic somite cells. 



The histological differentiation, as too the separa- 

 tion of the mesoblastic somites, is continually less 

 and less defined the further back the mesoblastic 

 somites lie, which we observe in the series of 

 transverse sections. If we consider the section re- 

 presented in Fig. 89 through the third mesoblastic 

 somite, and that represented in Fig. 90 through, 

 the fourth, we can see how gradually the movement 

 of the cells take place which lead to complete separa- 

 tion of the mesoblastic somite. 



As we have already recognised from the back view 

 of the whole embryo (Fig. 47). the lumens of the 

 individual mesoblastic somites are fully separated 

 from one another. Those sections therefore also r 

 which are constructed in the region between two 

 mesoblastic somites, must show an altered appearance. 

 "We see here the mesoblastic somites cut straight . 

 through, and we see too that here the slit which 

 leads into the inside of the mesoblast fold is closed 

 by union of the median dorsal hypoblast plate with 

 the ventral hypoblast. Nevertheless the place where 

 the closing happens is still distinctly to be seen. 



