micropyle

The micropyle is a small opening or pore in the ovule of seed plants or in the eggshell of some animals. In flowering plants, the micropyle is the opening at the apex of the ovule, usually near the point where the integuments meet. It is formed by the inner and outer integuments and marks the route by which the pollen tube can access the embryo sac for fertilization. The pollen tube typically grows toward the ovule and enters the embryo sac via the micropyle canal to deliver sperm cells. After fertilization, the micropyle may remain as a pore in the mature ovule or seed, sometimes becoming sealed by tissues during seed coat formation.

In animal reproduction, the micropyle is a specialized pore or channel in the eggshell that permits sperm entry in eggs of many insects and some other invertebrates. The location and structure of the micropyle vary among taxa, but its core function is to restrict sperm access to the egg while enabling fertilization. In some species, the micropyle is formed during oogenesis by follicle cells and becomes the sole route for sperm penetration.

The term is sometimes extended to describe analogous openings in other organisms where fertilization occurs through a defined pore. Overall, the micropyle is a controlled gateway that facilitates selective sperm entry while maintaining the integrity of the protecting coverings.