2 3 8 PAULINE H. DEDERER. 



PLATE II. 



FIG. 4. Portion of edge of ectodermal membrane, the cells almost completely 

 flattened and slightly curled back at their extreme edge; mesenchyme cells pro- 

 jecting beyond them. 



FIG. 5. Result of contraction of the ectoderm due to mechanical disturbance. 

 The dark mass at the left is a retracted membrane of ectoderm and mesenchyme. 

 Other portions of the mesenchyme remained adhering firmly to the cover-glass. 



FIG. 6. Group of ectoderm cells, with large nuclei and faintly granular cyto- 

 plasm. Nuclei of mesenchyme cells are smaller, and are surrounded by dark 

 granules derived from degenerated pigment cells; the boundaries of mesenchyme 

 cells are not visible. 



FIG. 7. Group of yolk cells lying upon the mesenchymal membrane where 

 they had migrated from the digestive tract. The yolk spheres are stained deep 

 black with hematoxylin. 



