Universlty of Manitoba, ln Partîal Fulfiìlment - MSpace at the ...

164
Hensenrs node and the primitive streak were stil I prominent, w¡th
no eví de¡ice of ta I I -bud format Ìon.
6.1.t+ Stagé 1l-12 Exöéf irhérital Embivos (Groun I l)
All experimental embryos showed retardation of neural closure.
ln general, the braÌn region was closed but the neural plate wss still
closlng over the somite and protosomlte areas, inverted or elevated at
the anter¡or rhomboid slnus, and elevated or flattened at the posterior
rhombold s inus .
One embryo (6E 34) showed definite eversion of the neural folds at
the posterîor rhomboid slnus, similar to the appearance of the two stage to
experimental embryos. Together with the retarded closure of the neural
folds was an appêrent delay ín appearânce of the overlap zone, as no
accessory canals were visible (f¡gs. 49 and 50)
ln other respects the appearances of these experîmental embryos resembled
those of the contro¡s, in that:
a) the rhombic roof was thîckened
b) ectoderm was in continuity with the neural folds
c) therê were no somitic mesoderm and few neural crest cells between
areas of cìosed neural tube and the overlyîng ectoderm
d) notochord was in close contact with the neurar tube over the somite,
protosomite, and anterior rhomboid sìnus areas, but not generally in the
brain regîon
e) somitic mesoderm was usually in contact ur¡th the neural tube in the
somite and protosomite areas, but not at the levels of unsegmented and
fused mesoderm
f) the somîtes were well-developed, wíth no cysts or hemorrhages and no
reduct ion in vo I ume.