GLYCOGEN IN CELLS OF EMBRYOS. 243 



The three regions which showed this color reaction will be dis- 

 cussed separately. 



1. Oval Cells. As the iodine vapor penetrated the hanging 

 drop, the cytoplasm of these cells became a pale yellow; then 

 the granular portion, including the mitochondria and fat droplets, 

 i.e., the endoplasm, appeared to shrink slightly and became a 

 deeper yellow. Meanwhile the remainder of the cytoplasm, 

 except a thin yellow ectosarc, turned pink, the color gradually 

 deepening until, after a few seconds, this portion was a deep 

 port-wine color, while the endoplasm, nucleus and ectosarc 

 remained yellow. At times the port-wine-colored material 

 occupied the greater part of the cell, leaving only a small clump 

 of endoplasm and the nucleus. In other cases the yellow endo- 

 plasm, nucleus and ectoplasm took up practically the entire cell 

 except what appeared as a large port-wine-colored vacuole. The 

 contour of the cell did not change but remained the same size 

 as it was before exposure to the iodine. In a few of these cells 

 there were a number of vacuoles, which also became port-wine 

 color. The color was more intense in tone in the oval cells than 

 in any other portion of the growth. It remained in them for 

 some time, in a few instances for over an hour, then faded, and 

 the whole preparation became a dark yellow color. 



2. Mesenchyme Cells of the Membrane. Of the cells forming 

 the membrane probably only the mesenchyme exhibited the 

 port-wine color upon exposure to iodine. This was difficult to 

 determine definitely because the cells adhered together so closely, 

 and also because of the fact that, while the mesenchyme cells 

 were frequently found extended beyond the ectoderm cells, the 

 latter were never observed separated from the former. Not all 

 of the mesenchyme cells showed the port-wine color when in the 

 presence of iodine, and which ones would do so could not be 

 foretold. In these cells the cytoplasm of the central and thicker 

 portion of the cell became a diffuse pink color, while the nucleus 

 and ectoplasm became yellow. This area of pink coloration was 

 not definitely limited but toned off into an extensive yellow 

 ectoplasm. The arrangement of the mitochondria and other 

 structures was the same in the cells having a pink area as in 



