Fertilization observed

Fertilization was observed when a sperm cell entered an egg cell of a sea urchin, confirming that a union of both was necessary for the birth of young. This observation greatly advanced the understanding of reproductive biology.
 Oskar Wilhelm August Hertwig Germany 1875 Fertilization observed

Fertilization was observed when a sperm cell entered an egg cell of a sea urchin, confirming that a union of both was necessary for the birth of young. This observation greatly advanced the understanding of reproductive biology.