ß4 ^- MITSUKURI; 



Series XII, 

 (PI. VI.) 



Trio)ujx japonicus. 



An emlnijo with about 15 mcsohlastic somites ; talien out 10^ J2 days 

 after deposition ; represented in Figs. 26 (PL III.) and 26a (I'l. II.). 



In this embryo, not only is the tail-swelling already well 

 developed but the allantois has made considerable progress in 

 development. 



a is in front of the anterior end of the nenrenteric canal. 



The medallary chord, tlie notochord, and the hypoblast 



are already united togetlier. 

 b is three sections behind a and is the second section in 



which the neurenteric canal is open below. The meso- 



blast is united with the wall of the neurenteric canal for a 



short extent 

 C is five sections behind h and is the first in which the 



neurenteric canal is closed below. The wall of the canal 



is still reco2:nisable, althouo'h united with the mesoblast 



alonsf its whole heio'ht. 

 d is five sections behind c. There is still a trace of the wall 



of the neurenteric canal in the most dorsal part of the 



" Endwulst." There is a bay in the hypoblast. 

 e is tAvo sections behind d. The " Endwulst " mass is 



divided into two ]nasses, an upper and lower. The 



upper is the tail itself and the lower the allantoic mass. 



In the latter, there is a deep bay from the enteron below. 

 f is two sections behind e and is very much like that section, 



but the allantoic bay is now cut off from the enteron 



below. Note that in c-J\ the lateral plates are below 



and not included in the tail-swelling. 

 g is two sections behind f. The upjer mass of the " End- 



