Less than 10.
It makes perfect sense.
Testicles store semen.
This has to be 'maintained' at a 'correct' temperature by the body to be most effective.
The testicles do this by utilising the sack, either drawing it up (too cold) or letting ur nuts hang (too hot)
If the wrinkles were not there your sack would be permanently tucked under your tiny penis.
It wouldn't be able to regulate because those wrinkles are where the skin expands.
Your jizz would be useless.
Learn moar biology.
You're welcome.