Henneberg, Maciej, and Jerzy Kozak. “Seasonal Rythm of Births in an Rural XIXth Century Population: Parish of Szczepanowo (Bydgoszcz Voivodeship)”. Anthropological Review, vol. 42, no. 1, Jan. 1976, pp. 19-31, doi:10.18778/1898-6773.42.1.02.