A testicle that doesn't move down into its proper place in the scrotum before birth is called an undescended testicle. It's also known as cryptorchidism (krip-TOR-kih-diz-um). Most often, it's just one testicle that doesn't descend into the scrotum, which is the bag of skin that hangs below the penis. But sometimes both testicles are affected. More @Wikipedia
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