429 
the epiblast and its derivatives of the future animal 
are derived. In the region of the primitive plate and 
its anterior enlargement are producedthe archenteron, 
the yolk-plug!), the notochord, the mesoblast, both 
peristomal and gastral, the definitive hypoblast and 
its derivatives. The primitive lower layer contributes to the 
embryo-body only so far as some of its cells are unrecognizably mixed 
up with the cells of the primitive knob, when the latter spreads itself 
on the ventral surface of the embryonic shield. 
In the light of the results obtained above, we may represent the 
Chelonian egg diagrammatically as in fig. 7. Its similarity to the 
well-known section of the Amphibian egg given by Hertwie (fig. 8) 
Fig. 7. 
is so evident that I need not stop to point it out. In establishing 
the homology of a Reptilian with an Amphibian or Ichthyopsidan egg, 
1) For the description of the yolk-plug see Mirsuxuri and IsHikawa 
“On the Formation of the Germinal Layers in Chelonia”. Quart. Journ. 
Microsc. Sc., Vol. 27. Also in the Journ. Se. Coll., Vol. 1. Rosınson and 
AssHETON (“The Formation and Fate of the Primitive Streak etc.” Quart. 
Journ. Microsc. Sc., Vol. 32) object to regarding this structure as the yolk- 
plug. I simply state here that I see no reason to modify our views. 
