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4. 4) Field, The Development of the Pronephros and Segmental Duct in Amphibia. Bull. Mus. Comp. Zoology at Harvard College 21. 1891.
5. 5) Filatow, Zur Entwicklungsgeschichte des Excretionssystems bei den Amphibien. Anat. Anz. Bd. 25. 1904.