236 PAULINE H. DEDERER. 



PLATE I. 



FIG. i. Seven-day culture from 1 5-day embryo, showing extent of double 

 membrane composed of ectoderm and mesenchyme. The latter projects beyond 

 the thickened edge of the ectoderm in the form of a loose reticulum or of isolated 

 cells. 



FIG. 2. Portion of outgrowth from an explant showing a continuous ectodermal 

 membrane of large flat cells, and an imperfect membrane of darker granular 

 mesenchyme cells, which lies above it. 



FIG. 3. Portion of a reticulum of elongated mesenchyme cells, attached at one 

 end to the thickened edge of the ectoderm, anchored at the other to the cover-glass 

 by broad fan-shaped expansions. In some of the ectoderm cells delicate striations 

 are visible. 



