Based on the success of earlier lectures, in 1859 Wagner began construction on a building that would become the permanent home for his collections and his educational program. Designed by Philadelphia architect John McArthur, Jr., who later designed City Hall, the building was completed and opened to the public in 1865.

THE LEIDY ERA | Wagner continued to lecture and lead the unique institution he had founded until his death in 1885. Direction then passed to a Board of Trustees who appointed Dr. Joseph Leidy (1823-1891), a biologist of international reputation, to head its scientific and educational programs. Joseph Leidy’s appointment ushered in an active and productive era in which the Institute’s mission and programs were greatly expanded. He invigorated the public lectures by retaining some of the most noted scientists and explorers of the day for the faculty. Leidy also added original scientific research to the Institute’s programs and organized its earliest field expeditions. The results of this work were published in the Institute’s own publication, The Transactions of the Wagner Free Institute of Science.

Leidy’s most lasting and significant contribution to the Institute, however, was his reorganization of the museum. Wagner’s original collections had been greatly enlarged by specimens collected in the field and through purchases and acquisitions. Leidy personally developed and supervised their reorganization into a systematic display in which specimens and cases were arranged so that visitors and researchers moved from simpler to more complex organisms and through geologic time as they walked through the exhibition hall. This new display opened in 1891 and little has been altered since Leidy’s time, making the Institute an exceptional example of a Victorian science museum.