60 k:- mitsukurI; 



Series XI. 

 (I'i. IX.) 



Cleniiiuis japunica . 



An emhri/o iritli about 13 mesohlastic somites ; taken out 8 daijs after 

 deposition ; like that represented in Fiij. 15 (PL IL). (xxxxiii ®) 



The tail-swelling is very distinctly arisen. The posterior tube 

 of the amnion is produced to a length about two-thirds that of the 

 embryo proper. 



a is from the posterior dorsal region. The medullary chord 

 and the notochord show the first sio^n of fusion l3y the 

 presence of a few spindle-shaped cells at the boundary 

 between the two. 



b is ten sections behind a. The medullary chord, the noto- 

 chord, and the hypoblast are united together. 



C is two sections behind /*, and is the first in which the 

 neurenteric canal is open below. Two liemi-clwrdae are 

 distinctly recognisable. 



d is five sections behind c. The posterior limit of the neu- 

 renteric canal is reached and it is just closing. The 

 mesoblast of both sides is united with the wall of the 

 neurenteric canal. Note that, from a backwards, the 

 dorsum of the sections is much more arched than in 

 Series X. This is necessary in order to pass to the now 

 elevated tail-swellino. 



o 



e is four sections behind d. The posterior part of the neu- 

 renteric canal is still distinct. The middle portion of the 

 section enclosing the " Endwulst" is Cjuite high. 



f is two sections behind e. The last vestiges of the wall of 

 the neurenteric canal are present. 



g is next behind /. The '' Endwulst " is now homogeneous, 

 except for a crowding of cells in its middle caused by the 

 very last vestiges of the wall of the neurenteric canal. 



