n.
In vertebrates, common chamber and outlet into which the intestinal, urinary, and genital tracts open.
It is present in amphibians , reptiles , birds , some fishes (e.g., sharks ), and monotreme mammals but is absent in placental mammals and most bony fishes. Certain animals (e.g., many reptiles and some birds, including ducks ) have an accessory organ (penis) within the cloaca that is used to direct the sperm into the female's cloaca. Most birds mate by joining their cloacas in a "cloacal kiss"; muscular contractions transfer the sperm from the male to the female.