1. Allen, J. A., The influence of physical conditions on the genesis of species. Radical Review, 1. 1877.
2. Allen, J. A., The evolution of species through climatic conditions. Science, N. S. vol. XXII, No. 569.
3. Bartholomew, Physical Atlas. London 1899.
4. Beebe, Geographic variation in birds with especial reference to the effects of humidity. Zoologica: N. Y. Zool. Soc. Vol. I. No. 1.
5. Bogdanow, Compt. rend. Ac. Sci. Paris 1857.