40 



CHARLES R. STOCKARD 



Fig. 33 A still more posterior section through the same seventy-two hour 

 embryo as figures 31 and 32. This section is posterior to the place where the 

 intermediate cell mass and gut endoderm fades out into the indifferent cell mass, 

 EB, which may be considered to represent the end-bud mass; Pb, the yolk peri- 

 blast. 



The condition in the seventy-two hour embryo is, of course, 

 quite early and the cells are not yet as a rule taken into the cir- 

 culation. The appearance shown in these figures is exactly that 

 of very slightly younger normal embryos in which a circulation 

 would later be established. The figures, however, were made 

 from sections of an embryo that had no heart beat at the time of 

 its fixation, and, therefore, there is no chance that any of these 

 cells could have become misplaced by having been circulated 

 or carried about. 



The most careful study with the highest power of the micro- 

 scope has failed to reveal any type of cell in the intermediate 

 cell mass other than the early erythroblast, and in later condi- 



