The mighty Muscovy duck: Unlike mammals and turtles, for example, a male Muscovy duck uses lymph instead of blood to inflate his penis, which he can do in a third of a second, a new study shows. Also unlike mammals, the semen does not travel through an internal channel. Instead, it travels along an external groove that closes into a tunnel as lymph inflates the penis. The unusual anatomy and rapid eversion are probably the male duck's means of countering equally unusual female anatomy.
Found in "Sexual conflict takes shape in ducks" online at: sciencenews.org/view/generic/id/51448/title/Sexual_conflict_takes_shape_in_ducks
