Internal Hydrostatic Pressure of the Fundulus Egg

By means of a mercury manometer connected to a micropipette, the internal hydrostatic pressure of the unfertilized Fundulus egg was measured. Upon activation of the egg by micropuncture when the platelets in the cortex of the egg proper disappeared, there was a progressively increasing internal pressure which finally stabilized at 150 mm. Hg. The pressure was accompanied by the formation of a perivitelline space which contained a clear, colloidal material. The measured internal hydrostatic pressure of the egg was diminished by any means which decreased the perivitelline space. It was concluded that the perivitelline substance is the chief factor contributing to the pressure. The changes in volume of the egg proper are inversely proportional to the size of the perivitelline space, indicating that the surface of the egg proper is permeable to water.