Original: However, the interiors of Great Dark Spots are relatively cloud-free, and unlike Jupiter's spot, which has lasted for hundreds of years, their lifetimes appear to be much shorter, forming and dissipating once every few years or so.
Simplified: However, the insides of Great Dark Spots are mostly cloud-free, and unlike Jupiter's spot, which has lasted for hundreds of years, their lifetimes appear to be much shorter, forming and disappearing once every few years or so.