On spontaneous skin tumours in amphibia.

In 7 from 320 Rana temporaria grass frogs and 16 from 978 Rana ridibunda pond frogs, the 31 and 47 spontaneous skin tumors respectively, were observed. The tumors were represented by cystadenopapillomas and adenocarcinomas, and developed from epithelium of skin mucous glands. The spontaneous pigment tumors (melanophoromas) were found in 2 axolotls Ambistoma mexicanum. These tumors developed from hyperplastic melanophores in pigment spots and focal proliferations of melanophores located deeply in derma.