no teeth. In many amphibians there are also vomerine teeth attached to a facial bone in the roof of the mouth. The tiger salamander (Ambystoma tigrinum) is typical of the frogs and salamanders that hide under cover ready to ambush unwary invertebrates. Others amphibians, such as the Bufo spp. toads, actively search for prey, while the Argentine horned frog (Ceratophrys ornata) lures inquisitive prey closer by raising its hind feet over its back and vibrating its yellow toes. Among leaf litter frogs in Panama, frogs that actively hunt prey have narrow mouths and are slim, often brightly coloured and toxic, while ambushers have wide mouths and are broad and well-camouflaged. Caecilians do not flick their tongues, but catch their prey by grabbing it with their slightly backward-pointing teeth. The struggles of the prey and further jaw movements work it inwards and the caecilian usually retreats into its burrow. The subdued prey is gulped down whole. When they are newly hatched, frog larvae feed on the yolk of the egg. When this is exhausted some move on to feed on bacteria, algal crusts, detritus and raspings from submerged plants. Water is drawn in through their mouths, which are usually at the bottom of their heads, and passes through branchial food traps between their mouths and their gills where fine particles are trapped in mucus and filtered out. Others have specialised mouthparts consisting of a horny beak edged by several rows of labial teeth. They scrape and bite food of many kinds as well as stirring up the bottom sediment, filtering out larger particles with the papillae around their mouths. Some, such as the spadefoot toads, have strong biting jaws and are carnivorous or even cannibalistic. Vocalization The calls made by caecilians and salamanders are limited to occasional soft squeaks, grunts or hisses and have not been much studied. A clicking sound sometimes produced by caecilians may be a means of orientation, as in bats, or a form of communication. Most salamanders are considered voiceless, but the California giant salamander (Dicamptodon ensatus) has vocal cords and can produce a rattling or barking sound. Some species of salamander emit a quiet squeak or yelp if attacked. Frogs are much more vocal, especially during the breeding season when they use their voices to attract mates. The presence of a particular species in an area may be more easily discerned by its characteristic call than