In vertebrates, other than mammals, the passageway from the ovaries to the outside of the body is known as the oviduct. In female mammals this is known as the Fallopian tube. The eggs travel along the oviduct. These eggs will either be fertilized by sperm to become a zygote, or will degenerate in the body. Normally, these are paired structures, but in birds and some cartilaginous fishes, one or the other side fails to develop (together with the corresponding ovary), and only one functional oviduct is found.