The shape of the aboral and oral ectoderm
and the ciliary band that comprise the ADL, particularly in relation to the distribution and orientation of putative sensory cells therein, evokes a functional morphological explanation.
The resulting bucconasal membrane, consisting of a layer each of ectoderm
and endoderm, separates the two compartments.
No one has yet been able to induce the cells to form the three distinct germ layers, in the correct order: endoderm on the inside, mesoderm in the middle and ectoderm
on the outside.
(3) During the 3-5 weeks of gestational age neurulation occurs during which formation of the neural groove, closure of the anterior (25 days) and posterior (27 to 28 days) neuropores, appearance of the ventral horn cells, formation of anterior and posterior roots and disjunction of the neuroectoderm from the surface ectoderm
The cell bodies of the diffuse nervous system of the larva lie in the apical plate and around the ciliated band that borders the oral ectoderm
. Axons extend beneath the ciliated bands and to the muscles derived from the coeloms (Lacalli and West, 1993).
Teratomas are primary congenital tumors made up of tissue that arises from all three embryonic germ cell layers: the ectoderm
, the endoderm, and the mesoderm (although there have been reports of tumors made up of only bidermal ingredients).
The pluripotent cells of the embryo organize themselves at an early stage in germ layers: the endoderm, mesoderm and ectoderm
They are usually unilateral, unilocular, smooth- surfaced lesions filled with fatty material, containing tissues from all three embryonic layers- endoderm, mesoderm and ectoderm
This specification occurs at the end of gastrulation, when the region that will form the future neural crest encompasses the border strip of the embryonic ectoderm
and is situated at the interface between the neural and adjacent non-neural territories.
The tongue comprises two parts that have different embryologic origins; the anterior two-thirds of the tongue arise from the ectoderm
and the posterior one-third from the endoderm.
These totipotent cells can differentiate into tissue components representing derivatives of mesoderm, ectoderm
At 24 h, the assays were scored as fusions if the polyps fused to create a single gastric cavity and common ectoderm
, or as rejections if they fell apart.