The mouth of the tadpoles of Anura is furnished with horny armaments, substitutes for teeth. Their development and that of the mouth in general has been well described by Gutzeit.[30] In the young larvae of _Rana temporaria_, one or two days after hatching, a shallow groove appears above the conspicuous pair of adhesive organs. The groove becomes rhombic in outline, and when the mouth has been formed in its centre, the jaws appear in the median corners of the rhombus. The epidermis then rises like a circular wall around the jaws, and divides into an upper and lower lip; furrows appear on them, and between these various papillae and comb-like transverse plates of teeth. The papillae are possibly tactile organs, but although nerves enter them, nerve-endings of a sensory nature have not yet been discovered. On the fourth day the jaws become black, by the tenth day horny teeth have appeared upon all the plates of the mouth-armature, and on the seventeenth day the mouth-apparatus has reached the configuration typical of the tadpole, which is now about 14 mm. long. The number of horny teeth in _R. temporaria_ amounts to about 640. These teeth are not cuticular products, but cornified cells; they are very small, and consist each of one horny cell, which is shaped like a nightcap, the apex of which is curved back and serrated. The little teeth are shed continuously, {59}the renewal taking place by successive cells growing into the bases of the older series. The shape and size differ much in the various genera and species. The comb-like plates, composed of those teeth which surround the lips, seem to be used chiefly for the fixing or hooking of the food, while those which compose the horny beak proper, the armature of the jaws, are used like the radulae of snails. These beaks are likewise composed of a great number of individual teeth, closely packed together in several rows, but the teeth themselves are simple and not serrated. In _Hyla arborea_ there are in all about 560 teeth. The development of the mouth does not begin before the eleventh day; the horny teeth break through, and the jaws get black edges, on the eighteenth. In _Pelobates fuscus_ the number of horny teeth is increased to about 1100. In _Borborocoetes taeniatus_ the horny teeth form series of five bells, which fit into each other like the joints of a rattlesnake's tail.