pectinifera appears to develop in the following order: (1) differentiation of the coelomic pouches, (2) immigration of presumptive muscle cells from the coelomic pouches to the
blastocoel, (3) migration of the muscles along an extracellular matrix to the esophageal basement membrane, (4) extension of pseudopodia containing F-actin on the basement membrane, (5) growth of pseudopodia from the primitive muscle cells, (6) development of primitive muscles into the circumesophagus muscles that run parallel to each other, and (7) development of some oblique circumesophagus muscles on the parallel bundles.
Gastrulation clearly takes place by invagination: vegetal cells constrict at their apical ends as their basal regions extend into the
blastocoel (Fig.
However, we did not observe any PMC descendants maintaining strong expression of the antigen and migrating in the
blastocoel to form new spicules.
During the gastrula stage, lipid droplets were extruded into the
blastocoel (Figs.
excentricus blastulae during development indicates that density regulation is occurring as early as the 7th cleavage, when the
blastocoel begins to take shape (about the same time intercellular junctions are forming; Okazaki, 1975).
3D), and primary mesenchyme cells in the vegetal pole wall are set free into the
blastocoel (Fig.
ballii, blastomeres containing zooxanthellae move into the
blastocoel of developing embryos, eventually filling the space and forming a stereogastrula (Hirose et al.
The wide archenteron greatly reduces the
blastocoel.
The gastral cavity is different in origin and structure from the central cavity of coeloblastulae, which is a retained
blastocoel (Borojevic, 1969).
During primary invagination, the thickened vegetal plate buckles into the
blastocoel and gives rise to a short stub-like gut rudiment.
The
blastocoel disappeared at about 5 h after the first cleava ge, and the central region of the embryo was filled with cells containing either zooxantheline or lipid droplets, forming a stereogastrula.
For example, although calcium is known to participate in the early events of fertilization (1) and also plays a brief but critical role at each cleavage (2, 3), the regulation of transmembrane calcium flux during the interim between cleavages or during
blastocoel formation is unknown.
