FATE OF BLASTOPORE, ETC., IX CHELOXIA. 



43 



OILS with the nieduUurj chord above, Avith the mesoblast 

 on the right (apparent left) side, and with the gut- 

 hypoblast below. 



is four sections behind h and is the first in which the 

 neurenteric canal is open below. On the dorsal surface 

 of this canal is seen the section of the anterior termina- 

 tion of the yolk-plug, which is independent of any adjacent 

 structure. The section is slightly oblicfue : hence the 

 asymmetry of the yoliv-plug. 



IS five sections behind c. The neurenteric canal is closino- 

 below. On the median line above, is a fa nn el- shaped 

 depression and in it rests a triangular mass — the section 

 of the yolk-plug. As karyokinetic figures seemed especi- 

 ally numerous in this section, their phices have been 

 indicated. 



is two sections behind J,. AVe are entirely out of the 

 region of the medullary chord. There is a median 

 groove that goes from above deep into the " Endwulst." 

 We must regard this as the rudimentary primitive 

 groove. The section of the yolk-plug rests like a wedge 

 on the funnel-shaped upper part of this groove. 



is two sections behind e. There is no deep median groove 

 in the " Endwulst," but the epiblast is still continuous 

 with the mass below in the meditm line. The section of 

 the yolk-plug rests in a depression of the surface. 



is the second section behind /'. The yolk-plug is continu- 

 ous on the right (the left of the figure) with tlie epiblast, 

 while still marked by a groove on the left. The epiblast 

 is continuous w^ith the mesoblast below in the median 

 line. 



is five sections l)ehind g. The yolk-plug does not stand 

 out prominently but its extent (comprised between two 

 stars in the figure) is easily recognised by the peculiar 

 arrangement of cells unlike that of the epiblast — 

 the nuclei being packed without order. The lower face 



