| On February 21 & 22, 2001 we again followed gastrulation in an albino frog, but this time with a field of view of 1.5 mm x 1.5 mm, encompassing the entire embryo, about 1.2 mm in diameter. The depth was increased to 1.5 mm, allowing the visualization of the blastocoel/yolk interface. However, the yolk is too highly scattering to allow light penetration all the way through the embryo. The movie above follows the time evolution of a 150 micron thick vertical slice through the embryo. The slice is parallel to the animal-vegetal axis, but forms a 45 degree angle with the dorsal midline. The involuting mesoderm is clearly visible as it spreads dorsally and also ventrally until it forms the mesodermal mantle, a complete spherical shell under the ectoderm, and finally encloses the endoderm (yolk cells). |