254 



K. MITSUKURI. 



This, let us suppose, is surrounded by a layer of cells (although in 

 point of fact the lower pole is not enclosed until a much later 

 period), except at the point C where there is a mass of cells in 

 which both the epiblast and the layer surrounding the yolk are 

 merged. This is the Primitive Plate or Knob. Tn this knob, 

 there arises an invagination, B (Woodcut III. 2) which grows forwards 

 together with the anterior elongation of the primitive knob. Assume 



Woodcut III. 



