The spawning pool is a pit of primordial ooze which contains the genetic makeup of the zergling, and makes possible several zergling evolutions that increase their speed and attack rate. It likewise carries the genome bank for core colony organisms. A core feature of any hive cluster, the spawning pools are all modeled after the first spawning pool on Zerus, the pool of ooze where the very first zerg emerged and consumed essence to evolve. The Dominion stresses that any marines that succeed in penetrating a zerg hive cluster should make the spawning pool a high-priority target, for if the zerg's ability to spawn zerglings is crippled, the Swarm's ability to spawn overwhelming numbers of units is also crippled.
The spawning pool gives larvae the ability to morph into zerglings and the hatchery the ability to evolve into the lair. The spawning pool is also responsible for evolving the zergling with Metabolic Boost (faster movement) and Adrenal Glands (faster attack).
As in Versus mode, Kerrigan and Zagara still unlock the same units and static defenses from this structure. However, it morphs faster and gains an additional zergling upgrade for each of the Lair and Hive stages. In terms of structures unlocked, neither of these commanders have access to the Roach Warren (instead relying more on their hero units than the roaches), although Zagara's spawning pool will still unlock the Baneling Nest to allow the morphing of her zerglings. Zagara also researches bile launcher upgrades at this structure.
The spawning pool was visually updated during the first pass of creating final artwork for StarCraft II. The main difference was artistic direction asking for a single large pool rather than the numerous smaller pools seen in the original game. The beating heart in the center was an afterthought to make the design more interesting. It was desired that the intestines have a more "veins pumping look" but the water obscured it too much for this to be implemented.
The research to unlock the ability for zerglings to morph into banelings was once possessed by the spawning pool.