Cita APA (7a ed.)

Darwin, C. R., & Darwin, C. (1977). The origin of species: By means of natural selection ; The descent of man : and selection in relation to sex. Encyclopaedia Britannica.

Cita Chicago Style (17a ed.)

Darwin, Charles Robert, y Charles Darwin. The Origin of Species: By Means of Natural Selection ; The Descent of Man : And Selection in Relation to Sex. Chicago: Encyclopaedia Britannica, 1977.

Cita MLA (8a ed.)

Darwin, Charles Robert, y Charles Darwin. The Origin of Species: By Means of Natural Selection ; The Descent of Man : And Selection in Relation to Sex. Encyclopaedia Britannica, 1977.