Answer) The early developmental stage of an animal, while it is in the egg or within the uterus of the mother, is known as the embryo. In humans the term is applied to the unborn child until the end of the seventh week from the eighth week, the unborn child is called a fetus.For now, you can suppose surrogate situations where the mother is not available to carry, an animal does not need to be a better surrogate than a human, just as viable (or nearly so) as a human surrogate in situations where no human is available to be a surrogate.