136 



AGE, GROWTH, AND DEATH 



if we saw the cell isolated under the microscope, we 

 could determine from what part of the young em- 

 bryonic body it was derived. When we see a cell 



. - 





^g.^3s^ 



.' . 



FIG. 47. THREE SECTIONS THROUGH A RABBIT EMBRYO OF SEVEN AND 

 ONE HALF DAYS. For explanation, see Fig. 9, of which this is a repetition. 



from the adult we can determine its origin in most 

 cases with certainty by its microscopic appearance 



