Most animals needing a vagina make do with one. Some animals - by accident or intention - finish up with two. In the duck bill, the spiny anteater (i.e. in the monotremes), and in the marsupials the vaginas are paired, as are various other bits and pieces in the female genital arrangement. In the embryo the uterine tube, uterus and vagina exist as paired and entirely separate structures - and so they. remain in adults of the species mentioned. This "paired" feature - common to some animals can appear as an abnormality, prohibiting reproduction, in others. Where there is a congenital fault a female may be born with a double uterus and inadequate channels to a double or single vagina. In humans surgery can be attempted.