1. F. Süffert, Z. Morph. Ökol. Tiere26, H. 1/2 (1938).
2. L. de Ruiter,Countershading in Caterpillars. An Analysis of its Adaptive Significance. Thesis Groningen (1955).
3. W. B. Alexander,Die Vögel der Meere (Paul Parey, Berlin 1959), p. 221.
4. J. Huxley,Protective and other Coloration. Rep. from the Encyclopaedia of British Birds (The Waverley Book Co., Ltd., 1954), p. 406.
5. E. Trewavas, An. and Mag. of Nat. Hist.1, Series 11, 435 (1938).