The males of many species of frogs and toads have a pair of small vocal sacs or pouches which open into the mouth. Their principal use is to increase the volume of the voice when the frogs croak, the sacs become greatly distended with air; at other times they are not noticeable.
One group of cricket frogs in South America, whose pouches open from the floor of the mouth, has found a unique use for them-they carry the eggs in these sacs.
During the incubation period, the pouches become so enlarged that they extend well over the undersurface of the body. The embryos remain in the pouches until they have con1pleted their development and emerge as small frogs.