The collection consists of writings, correspondence, and subject files of Dahlgren (Princeton Class of 1894), a professor in Princeton's Department of Biology. The collection contains his history of the department and his outlines of seminars in the biology and zoology departments. There is correspondence from colleagues, including Edwin Grant Conklin, Bradley M. Davis, H. E. Jordan, and J. Sterling Kingsley, and letters relating to the Apgar Club. The subject files have material on the Princeton Mosquito Committee (1914-1918), the Committee on University Extension (1915), and readings recommended to candidates for the degree of Ph.D. in biology (1915). Includes a manuscript from 1864 by Dahlgren's grandfather, John Adolphus Bernard Dahlgren.