1. Adam, H., Z. mikrosk.-anat. Forsch.60 (1954) 6.
2. Deuchar, E. M., Xenopus: The South African Clawed Frog, p. 175. Wiley, New York 1975.
3. Komnick, H., Wilhelm Roux Arch.153 (1961) 14.
4. Nieuwkoop, P. D., and Faber, J., Normal table of Xenopus laevis. North Holland Publ., Amsterdam 1967.
5. Kordylewski, L., Bull. Acad. Pol. Sci.17 (1969) 347.