Triple Reproductive Tract

Female kangaroos (and all marsupials) have a remarkable reproductive system: three vaginas and two uteruses.

Here's how it works: - Two lateral (side) vaginas receive sperm and transport it to the two uteruses - A central vagina is used for giving birth - Two uteruses can each carry a developing embryo

This allows kangaroos to be essentially perpetually pregnant. A female kangaroo can have: 1. An older joey living outside the pouch but still nursing 2. A young joey developing in the pouch 3. An embryo in "suspended animation" (embryonic diapause) in one uterus 4. A newly fertilized embryo in the other uterus

The embryonic diapause is fascinating — the embryo stops developing at about 100 cells and waits. When the pouch joey is old enough, hormones signal the embryo to resume development. About a day after the older joey leaves the pouch, the new baby is born.

Baby kangaroos (joeys) are born after just 33 days of pregnancy, emerging as tiny, underdeveloped creatures about the size of a jellybean. They crawl up to the pouch and attach to a nipple, where they continue developing for several more months.