m 



FA'l'E OF BLASTOPORE, ETC., IX CHELONIA. ce 



is two sectioiis behind /. We ;ire now near the posterior 

 end c)f tlie tail -swelling. The primitive groove is still 

 present and at its edges the epi blast is reflected down- 

 wards to become continuous with the mass within. The 

 latter is connected hy a small string of cells with the 

 mesoblast below in which there is now visible a line 

 running across from side to side through its middle, 

 dividing it into the parietal and visceral layers. 



is next toy. The posterior end of the tail-swelling is now 

 reached. As that part is cut tangentially, it is very hard 

 to distinguish the epiblast from the enclosed " Endwulst " 

 mass. The upper part is undoubtedly the epiblast ; and 

 tlie lower part, crowded with cells, has probably the two 

 elements represented, although it is impossible to fix 

 the limits. The primitive groove is distinct. Below the 

 tail-swelling, the epiblast now goes entirely across from 

 side to side. The tail-swelling, the epiblast, and the 

 mesoblast seem to be united together in the median 

 line. 



is two sections behind k The very tip of the tail- 

 swelling is cut tangentially. The fact that the tail 

 appears as two masses is due to the circumstance 

 that the primitive groove goes from the dorsal surface 

 around the tip of the tail to the ventral surface, and 

 this section has cut the groove longitudinally at the tip. 

 The two masses consist evidently of the epiblast. The 

 epiblast below the tail is very granular in the median 

 line. I can not make myself sure whether this granular 

 part is continuous w4th the mesoblast IdcIow or not. 

 On the whole it seems to be not continuous, 

 is next to /. We are now clear of the tail-swelling, and 

 in the region of the posterior tube of the amnion. Hence, 

 there is only a clear tube without any structure enclosed 

 in it. I can not be certain whether there is any connec- 

 tion between the epiblast and the mesoblast in the 



