Fig. 4
From: A review of the reproductive system in anuran amphibians
Typically, non-reproductive structures are used as oocyte incubators in some frogs. Larval development and metamorphosis can occur within the vocal sac, where frogs incubate the eggs and secrete nutrients for embryo development (a). The females carry the eggs on their back and provide maternally derived nutrients via yolk (b). Gastric hatching frogs ingest fertilized eggs, after which they develop in the stomach and emerge as juvenile frogs (c)