Merian had seen Suriname Toads (Pipa pipa) in collections in Amsterdam. In Suriname she was able to study live specimens and to witness how the females incubate their eggs within ‘blisters’ in the skin of their backs. Merian was able to preserve one frog in brandy as some of the young hatched, and later used it to make an illustration which she included in the 'Metamorphosis'.