Sir

Naturally transparent: ventral view of a gravid female glass frog Hyalinobatrachium bergeri; snout–vent length 23 mm. Credit: I. DE LA RIVA

Your News in Brief story 'See-through frog offers inside information' (Nature 449, 521; 2007) reporting the creation of a transparent frog (Rana japonica) by M. Sumida and collaborators highlights an important achievement. But there are natural transparent tetrapods, which are not the result of genetic manipulation. The roughly 150 species of anurans commonly known as glass frogs (family Centrolenidae) show a high variation in degree of transparency, not only in their skin but also in the different peritonea covering their organs (see picture).

These natural 'see-through' frogs allow the observation in vivo of internal organs, which has potential for useful applications in the biomedical sciences. Further, although the transparent mutants of R. japonica are difficult to generate (only one out of 16 is transparent) and have very low fitness, glass frogs represent a highly diverse group wide-spread throughout the American tropics.

We know very little about these arboreal transparent frogs. But their potential use in biomedical research highlights the importance that should be attached to the exploration of biodiversity — as stressed in your 15 March 2007 issue, dedicated to Linnaeus's legacy.