Step 1: Understanding the Concept:
In the human male fetus, the testes develop within the abdominal cavity. Shortly before birth, they descend through the inguinal canal into the scrotum, where the temperature is lower ($2\text{--}2.5^\circ\text{C}$ below body temperature) to facilitate healthy sperm production.
Step 2: Detailed Explanation:
1. Cryptorchidism: This is the clinical term for "hidden testis." It occurs when one or both testes fail to descend into the scrotal sac. If not corrected, it can lead to sterility because the high internal body temperature inhibits spermatogenesis.
2. Atresia: Refers to the degeneration of ovarian follicles (follicular atresia) or the absence of a normal body opening.
3. Cretinism: A condition of severely stunted physical and mental growth due to untreated congenital deficiency of thyroid hormones.
4. Amenorrhea: The absence of menstruation in a woman of reproductive age.
Step 3: Final Answer
The failure of testes to descend is called Cryptorchidism.