It is not uncommon for the mucosal epithelium to
evaginate into the lumen to form villous projections (villi).
After ingestion, protoscolices emerge from the cyst,
evaginate, attach to the intestinal mucosa, and develop into adult tapeworms in the host's small intestine.
The fact that this system can
evaginate precociously in response to an ATP-containing medium (Hilfer and others 1977) implicates contractile forces in thyroid evagination and suggests an active role for microfilaments (Lewis 1955; Wessells and others 1971; Burnside 1973; Schroeder 1973) in the morphogenesis of this system.
Within as short a period as 15 min after rupture, the apical end narrows into a conical shape, and one to five tentacle primordia
evaginate in a ring below the apical tip [ILLUSTRATION FOR FIGURE 36 OMITTED].
Tentacles
evaginate from the head region and a mouth breaks through at the tip of the head, producing an immature polyp.
The embryonic lung
evaginates from the anterior endoderm which will form also the trachea and larynx.
The origin of placental teratoma is obscure but germ cell theory is widely accepted2 According to this theory in the early stages of embryogenesis the primitive gut
evaginates into the umbilical cord during which time primordial germ cells from the primitive gut migrate through the gut wall and are deposited in the connective tissue of the cord and eventually pass into connective tissue between amnion and fetal surface of
