PIECES OF FROG EMBRYOS CULTIVATED IN LYMPH. 



207 



near the center. At one side there was a thin vesicle filled with 

 fluid. The ectoderm cells covering this vesicle were much flat- 

 tened. Ten days later the whole piece was larger, owing to the 

 increase in the size of the hollow vesicle which had come to 



3 



FIG. 3. FIG. 4. 



FIG. 3. A piece which developed from a fragment of a middle portion of a frog 

 embryo. 



FIG. 4. The same piece as is shown in figure 3, but drawn ten days later. 



surround most of the rest of the fragment (Fig. 4). The pig- 

 mented mass and the tissue around it had assumed a more 

 nearly spherical form, and the whole structure had become more 

 nearly spherical also. Apparently the chief factor in the form 

 changes in this case was the absorption of fluid which caused the 

 increasing distension of the thin walled vesicle. A similar proc- 

 ess may account for the large spaces in the fragment shown in 

 Fig. 2. In transferring the nearly spherical fragment to fresh 

 lymph the thin wall of the vesicle partly collapsed, but it was 

 subsequently distended to its previous form. During the time 

 the piece was kept alive, which was about five weeks, it showed 

 no other marked changes in form. 



UNIVERSITY OF CALIFORNIA, 

 June 16, 1913. 



