fuscus has a stereoblastula
. At about the onset of gastrulation, the embryo developed a slight hump at the animal pole, and trochoblast cells began to produce patches of prototrocal cilia (Fig.
Embryos arrive in the pouch soon after fertilization, followed by formation of a stereoblastula
. The mode of gastrulation is not known.
The large amount of yolk contained within the eggs often results in the formation of a stereoblastula
that is solidly packed with cells (Uchida and Yamada, 1968).
Recently fertilized eggs were usually a stereoblastula
at the time of observation and were spherical with a smooth but not glossy surface; some were beginning to develop furrows.
About 26 days after fertilization, the stereoblastula is totally wrinkled [ILLUSTRATION FOR FIGURES 2E AND 4D OMITTED] and consists of a monostratified columnar epithelium enclosing a mesenchyme mass.
An incomplete and superficial segmentation becomes holoblastic and generates a wrinkled stereoblastula
After 12 h individual cells were no longer visible and the stereoblastula
exhibited a characteristic raisin-like wrinkled appearance.