Cita APA

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

Citación estilo Chicago

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

Cita MLA

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