Process of nuclear envelope reduction in spermiogenesis of a mosquito, Culex tigripes.

When the Culex tigripes spermatid begins to elongate, the nucleus exhibits on its surface invaginations of the nuclear envelope. These invaginations have a uniform diameter of 0.3 microns. They separate from the envelope of the nucleus and form spherical intranuclear vesicles. In the old spermatids these vesicles are imprisoned in the condensed chromatin. The spermatozoon also possesses these vesicles which are then ovoid in shape. This process of vesiculation permits the diminution of the surface of the nucleus when it decreases in volume during spermiogenesis.