48 '^' MITSUKURI; 



Series VI. 

 (Pi. Y.) 



Trioniix japoniciis. 



An emhrijo with about 10 mcsohlastic somites, taken out 8^J2 days after 

 depositioji ; repyescnted in Fig. 22 {PI. III.) and similar to Contrih. 11., 

 PI III., Figs. 19 & 19a. (113 h) 



a is from the hinder portion of the mid-clorsal region. 

 The medullary chord shows the first sign of fusion with 

 the noto-chord by the presence of two nuclei lying cross- 

 wise in the boundary between the two chords. 



b is two sections behind a. The two chords have now 

 fused with each other. 



C is thirteen sections behind h. The two chords, the hypo- 

 blast, and the mesoblast of the right side are fusing with 

 one another. 



d is two sections behind c and is the first in which the 

 neurenteric canal is open below. The mesoblast of the 

 left side is still independent, — due no doubt to the 

 obliquity of the section. 



e is six sections behind d. The Avail of the neurenteric 

 canal is now fused with the mesoblast by its whole sides. 



f is next to <'. The neurenteric cannl is just closed. Other- 

 wise it is like e. 



g is three sections behind /". It is out of the region of 

 the neurenteric canal. In the median dorsal line, 

 the epiblast appears to be connected with the mass 

 below for a short space. There is no primitive groove 

 in the median line. This corresponds to Series III., i, or 

 to Series V., i. 



h is eight sections behind g. In passing from g to //, the 

 " Endwulst " has been gradually diminishing, and in li, is 



