The following section contains information from a previous version of StarCraft II: Heart of the Swarm which is no longer valid.
Formerly called the evolution chamber, the structure enabled changes to units.
Each unit featured three upgrades and a final, irreversible choice. For instance, the zergling can get the Metabolic Boost, Posthumous Mitosis, and Rapid Genesis upgrades. Afterward it could become a raptor (which gains combat bonuses) or a swarmling (which spawn 3:1).