yolk cell

The shield extends over about 100 of the yolk cell surface.

Garpike, therefore, have a single yolk cell similar to that of teleosts.

Some of them are difficult to remove, for they are still attached by stalks to the yolk cell.

The vegetal half of the morula, the future yolk cell, still exhibits a smooth surface.

The blastoderm has an irregular rim and a flat bottom where it joins the yolk cell.

Dissection reveals a continuing presence of deep central cells that appear to be budding from the yolk cell.

Many central blastomeres are also separated from the yolk cell by tangential cleavage divisions.

Dissection shows that the deep blastoderm cells are still connected to the yolk cell, and appear to bud from it.

The exposed surface of the yolk cell now comprises a large yolk plug.

Many of them show broad connections with the yolk cell, and many join it via a narrow stalk.

In a 64-cell embryo, about 30 complete blastomeres appear on the surface, surrounded by marginal cells that are continuous with the yolk cell.

Cleavage furrows on the yolk cell are regressing by this time; they extend only to the egg's equator, no further.

The second furrow proceeds like the first, dividing the blastoderm deeply and extending past its margin outward across the gray yolk cell.

Unlike the teleostean pattern, however, the cleavage furrows continue past the blastoderm margin as grooves in the yolk cell surface.

This produces a slight bulge in the blastoderm margin at that location, as though epiboly were being retarded by its attachment to the yolk cell.

The blastoderm overhangs its margin at the dorsal midline, having a crinkled edge where it attaches to the yolk cell.

The exposed yolk cell surface beneath the dorsal lip is the first external appearance of the yolk syncytial layer.

The peripheral blastomeres of the YSL appear to maintain cytoplasmic bridges with the yolk cell.

In most other flatworms, yolk cells, where present at all, are typically formed in a gland derived from the ovary, but separate from it.

The blastoderm begins to thin as it spreads toward the vegetal pole of the embryo until it has completely engulfed the yolk cell.

However, in all these embryos there is diffuse labeling of the membrane of the yolk cell rather than labeling of platelets.

Ring-like structures of filamentous actin have been observed at the leading edge of the enveloping layer, where it contacts the yolk cell.

The first two grooves sometimes meet at the vegetal pole, but we found no evidence in living or fixed eggs that they extend significantly beneath the yolk cell cortex.

However, only one or two garpike cleavage furrows even extend to the vegetal pole, and these are nothing more than shallow grooves in the yolk cell cortex.

In most platyhelminths, the ovaries are divided into two regions, one producing the ova, and the other producing specialised yolk cells to nourish the developing embryo.