In the centre of this antipedal area there has appeared (often at a very early period) a gland-like depression or follicle of the integument.
When the follicle bursts, as it does in time, the ovum escapes on to the surface of the ovary.
In many embryo Lamellibranchs a centro-dorsal primitive shell-gland or follicle has been detected.
No regular follicle is formed, but the odcyte absorbs nutriment from the remaining odgonia.
The result of this process is a minute ovoid embryo consisting of a solid mass of cells surrounded by a follicle of flattened yolk-cells.