Sperm from the milt carry chromosomes. The chromosomes of the sperm carry the traits of the male. When the male and female chromosomes join, a new animal starts to grow. This is called fertilisation. To keep the egg and sperm alive before fertilization, animals must keep them wet.
All mammal fertilization happens inside the female's body in or near the uterus.
The uterus is a special organ that holds the newly forming animal. The new animal is called an embryo, and then a fetus while it grows inside its mother's body. While it is developing in the uterus, the embryo is connected to its mother by a placenta and umbilical cord. The placenta is a spongy growth where nourishment can go from the mother's blood vessels to the embryo's blood vessels without any exchange of blood. The placenta is attached to the inside of the uterus.