ANATOMICAL TRAVELOGUE / SCIENCE PHOTO LIBRARY ANATOMICAL TRAVELOGUE / SCIENCE PHOTO LIBRARY
Restrictions may apply. Please contact SPL for further details.
Computer artwork of sperm (spermatozoon, blue) attempting to penetrate a human egg (round). Women usually release one egg (ovum) per month, whereas men release millions of sperm in each ejaculation. Only one of these sperm can penetrate the egg's thick outer layer (zona pellucida) and fertilise it. Fertilisation occurs when the sperm's genetic material (deoxyribonucleic acid, DNA) fuses with the egg's DNA. When this occurs the egg forms a barrier to other sperm.
Model release not required. Property release not required.