by osmosis to supply the toad's needs. Spadefoot toads are "explosive breeders", all emerging from their burrows at the same time and converging on temporary pools, attracted to one of these by the calling of the first male to find a suitable breeding location. The burrowing frogs of Australia have a rather different lifestyle. The western spotted frog (Heleioporus albopunctatus) digs a burrow beside a river or in the bed of an ephemeral stream and regularly emerges to forage. Mating takes place and eggs are laid in a foam nest inside the burrow. The eggs partially develop there, but do not hatch until they are submerged following heavy rainfall. The tadpoles then swim out into the open water and rapidly complete their development. Madagascan burrowing frogs are less fossorial and mostly bury themselves in leaf litter. One of these, the green burrowing frog (Scaphiophryne marmorata), has a flattened head with a short snout and well-developed metatarsal tubercles on its hind feet to help with excavation. It also has greatly enlarged terminal discs on its fore feet that help it to clamber around in bushes. It breeds in temporary pools that form after rains. Climbing Tree frogs live high in the canopy, where they scramble around on the branches, twigs, and leaves, sometimes never coming down to earth. The "true" tree frogs belong to the family Hylidae, but members of other frog families have independently adopted an arboreal habit, a case of convergent evolution. These include the glass frogs (Centrolenidae), the bush frogs (Hyperoliidae), some of the narrow-mouthed frogs (Microhylidae), and the shrub frogs (Rhacophoridae). Most tree frogs are under in length, with long legs and long toes with adhesive pads on the tips. The surface of the toe pads is formed from a closely packed layer of flat-topped, hexagonal epidermal cells separated by grooves into which glands secrete mucus. These toe pads, moistened by the mucus, provide the grip on any wet or dry surface, including glass. The forces involved include boundary friction of the toe pad epidermis on the surface and also surface tension and viscosity. Tree frogs are very acrobatic and can catch insects while hanging by one toe from a twig or clutching onto the blade of a windswept reed. Some members of the subfamily Phyllomedusinae have opposable toes on their feet. The reticulated leaf frog (Phyllomedusa ayeaye) has a single opposed digit on each fore foot