area
pellucida
YOLK OF THE HEN'S EGG
,cell processes
celt bodies
251
primitive
streak
area
pellucida
I margin of
overgrowth
'syncyncytiaf
zone
inner zone
B
embryo
cell processes]
Imargin of
;^cell bodies jovergrowth
area vitellina
externa
area vasculosa
area vitellina
interna
FIG. 20. Diagrams illustrating the main regions of the area opaca at (A) about 18 h
and (B) about 48 h of incubation. See text for full description. (From Bellairs, 1963.)
deny this (see discussion by Hamilton, 1952). Meanwhile, the endoderm
cells of the inner zone have begun to arrange themselves in an epithelium oftall columnar cells (see Bellairs, 1963). The change has proceeded furthest in the most proximal cells and is less advanced in the
distal ones, which merge gradually into the area vitellina whose cells
are less closely packed.