D&Dtools1

Your body withers away to dust, leaving only a floating head, which quickly grows oversized and misshapen.
Your eyes fuse together as a single orb in your forehead, and ten writhing eyestalks sprout from your skull.
You take the form of a beholder (MM 26).
You gain 30 temporary hit points, which disappear at the end of the spell's duration.
You can use only one eye ray each round, and each of your ten eye rays can be used only once during the spell's duration.
For example, once you use your disintegrate eye ray, you can't use that eye ray again during this casting of the spell.
See the Polymorph Subschool sidebar on page 91 for more details.