Light micrograph of a human ovum in the fallopian tube. The ovum, or egg, is produced in the ovary, where it matures as a follicle in the body of the ovary, migrating to the surface prior to ovulation, when it enters the fallopian tube. It is here, in the outermost region, where conditions are chemically favourable, that potential fertilisation may occur. The ovum has a life expectancy of 12-24 hours, during which time one spermatozoon must penetrate the nucleus for fertilisation to take place.