APA (7th ed.) Citation

Haeckel, E. H. P. A., & McCabe, J. (1900). The riddle of the universe at the close of the nineteenth century. Harper.

Chicago Style (17th ed.) Citation

Haeckel, Ernst Heinrich Philipp August, and Joseph McCabe. The Riddle of the Universe at the Close of the Nineteenth Century. New York: Harper, 1900.

MLA (9th ed.) Citation

Haeckel, Ernst Heinrich Philipp August, and Joseph McCabe. The Riddle of the Universe at the Close of the Nineteenth Century. Harper, 1900.