In 1937, the bear exhibits were built under the Works Progress Administration. These exhibits were the zoo's first attempt at constructing more naturalistic exhibits instead of simply displaying animals in cages. In 1949, the Children's Zoo opened with a grant from the Sarah Mellon Scaife Foundation. The Children's Zoo contained interactive exhibits and play areas for children, including a simulated large chunk of cheese that was inhabited by dozens of live mice. In 1967, the AquaZoo, a large aquarium, opened to the public. At the time of its completion, the AquaZoo was the only aquarium in Pennsylvania and the second largest aquarium in the United States.