Goat and squirrel, Avissawella, Sri Lanka.

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What you see above are three pictures of a male squirrel. You can just make out the descended testis below the root of the tail. During the mating season the testis descends from inside the abdomen to the scrotum. The cold outside stimulates production of sperms. During the non-mating time the testis is drawn into the abdomen where the higher temperature suppresses sperm production. This new position of the testis inside the abdomen also protects it from injury. The squirrel jumping from branch to branch has a high chance of injuring its testis if the testis remains permanently outside the abdomen.