428 
formed the Notochord and the Gastral Mesoblast. (See my 
paper “Further Studies on the Germinal Layers of Chelonia”, Journ. 
Sc. Coll. Tökyö, Japan, Vol. V, Pt. 1.) 
5) The floor of the archenteron is divided into two parts: (a) 
the larger posterior part which proliferates the peristomal mesoblast, 
and (b) the smaller anterior part, which losing its definiteness is 
finally absorbed, together with that part of the primitive knob lying 
underneath it, thus putting the 
archenteron in communication 
eave. Shield BX. with the large subgerminal ca- 
vity in the yolk (fig. 4). 
6) The primitive knob which 
Arche. was gradually spreading itself 
beneath the embryonic shield 
RE. rs before the breaking through of 
3. the archenteric cavity continues 
to do so after that event, until 
ZA Cs > the whole of the ventral surface 
HF of the embryonic shield has been 
Fa covered when the process stops 
— =~ (fig. 5). The advance of the cells 
of the primitive knob is in its 
a later stages marked by a peri 
— — pheral reticulated zone with a 
6 compact central area. (See figs. 
un oa 4b—13b of Mennert’s “Gastru- 
_— lation u. Keimblatterbildung der 
Emys lutaria taurica”. Morph. 
Embr shield —Embryonce Shiela Arbeiten, herausgeg. v. Dr. G. 
ae — Archenleron.. SCHWALBE, I. Bd., 3. Heft. 
Vi a ene MEHNERT gives a different inter- 
ug Lok plug pretation to this appearance.) 
7) At some distance back 
from the anterior end of the embryonic shield, the head - fold is seen 
developed (fig. 6 Hd. fd.). As the primitive knob marks the posterior 
end of the embryo and the lateral folds arise within the embryonic 
shield, the conclusion is reached that the future embryo-body 
is developed entriely within the area covered ven- 
trally by the part derived from the primitive knob. 
If we put the results in another way, they may be summed up 
as follows: From the epiblast of the embryonic shield, 
basis ‘ 
