FATE OF BLASTOPORE, ETC., IX CHELOXIA. 47 



mass with a few nuclei. This is the anterior free point 

 of the yolk-plug. The epiblast is also changed 

 in character for a short extent in the median line, 

 being more granular, with nuclei scattered irregularly. 

 It is very difficult to decide whether there is any 

 connection between the epiblast and the mesoblast in 

 the section, but if it is present, it is certainly very slight. 

 On the whole, I consider that there is no such. 



m is five sections behind / and is the fourth of five similar 

 sections through the yolk-plug. The latter rises up from 

 below between what can be recognised as the lips of the 

 epiblast. Its similarity to Series I., /, or Series III., k, 

 is so great that it is only necessary to call attention to it. 

 The hypoblast is no longer a cellular layer in this section ; 

 it consists of a protoplasmic network with yolk-spherules 

 and nuclei imbedded in it. 



n is four sections behind m. In tracing the yolk-plug 

 backwards from such a section as m, we find it fusing 

 laterally with the epiblast but its place can be identified, 

 as it is coarsely granular and is also arched above, at first 

 very distinctly, then gradually less and less. In this 

 section, its place is indicated by two stars : it is already 

 only slightly arched. The layers are independent. One 

 or two sections behind, arching becouies hardly re- 

 cognisable. 



In this Ghclonia embryo, the primitive streak stretches from the 

 region of the neurenteric canal to the yolk-plug. The primitive 

 groove also begins at the posterior part of the medullary canal Avhich 

 is still open dorsal ly, and reaching over the entire length of the 

 primitive streak, widens out at the posterior end to allow the yolk- 

 plug to stick out between them. The yolk-plug is very distinct and 

 unmistakable, but its posterior limit can not be fixed definitely. 



