Both sexes have a cloaca similar to a chicken, i.e. only one opening for the digestive, urinary and reproductive systems. Since there are no external sex organs, observation of enlarged nipples can be used to identify a nursing female. Because the penis has a bone, X-rays or palpatation are other common methods. Another way is to express the anal glands of a tame, or immobilized animal. If the secretion is dark (brownish), then it is a male. If light (clear or whitish), it is a female.