SEM of human sperm and egg at the moment of penetration. After sperm makes contact with the egg's surface, the acrosome membrane at the sperm's tip fuses with the egg's plasma membrane releasing acrosome contents. A continuous membrane is formed between the sperm and the egg and the sperm's contents, including its nucleus, then begin to enter the egg's cytoplasm. Magnification: 4,000x @ 8x10inches.