Scanning electron microscopy of the vitelline membrane of the hen ovum

Manual removal of the perivitelline layer overlying the animal pole (AP) reveals three morphologically distinct regions of the vitelline membrane (VM). (1) The central germinal region is 600-800 micron in diameter and is densely populated with pleomorphic microvillous projections. (2) The periblastic region, which also exhibits microvillous projections, is 250-550 micron wide and consists of numerous (80-120) lacunae that are 10-60 micron in diameter and up to 20 micron in depth. (3) At the outer periblastic region, the microvillous projections are less numerous. In the vegetal hemisphere, the VM has few projections and occasionally is discontinuous.