The stratum corneum is mostly thin, but on many parts of the body, especially in Anura, the epidermal cells proliferate and form hard spikes or other rugosities, generally stained dark brown. With these may be grouped the nuptial excrescences so frequent in the Anura, especially on the rudiment of the thumb, and on the under surface of the joints of the fingers and toes. In many Anura, less frequently in the Urodela, the tips of the fingers and toes are encased in thicker horny sheaths, producing claws or nails. They are best developed among newts in _Onychodactylus_, among the Anura in _Xenopus_ and _Hymenochirus_. The horny covering of the metatarsal tubercles reaches its greatest size in {33}the digging spur or spade of _Pelobates_. In most of these cases the cutis is elevated into more or less wart-like papillae, covered, of course, by the proliferated and cornified epidermis. In the female of _Rana temporaria_ nearly the whole surface of the body becomes covered with rosy papillae during the breeding season. Similar nuptial excrescences are common, and are most noteworthy in the male of the Indian _Rana liebigi_. The epidermis also contains sense-organs. They attain their highest development in the larvae; later on they undergo a retrogressive change. Each of these sense-organs is a little cup-shaped papilla, visible to the naked eye. It is composed of elongated cells which form a mantle around some central cells, each of which ends in a stiff cilium perforating a thin, hyaline membrane which lines the bottom of the cup, and is perhaps the representation of the cuticula. These ciliated cells are connected with sensory fibres, the nerve entering at the bottom of the whole organ. The cilia are in direct contact with the water, but the outer rim of the whole apparatus is protected by a short tube of hyaline cuticula-like secretion. These sense-organs are, in the larvae, scattered over the head, especially near the mouth and around the eyes, whence they extend backwards on to the tail, mostly in three pairs of longitudinal rows, one near the vertebral column, the others lateral. They are supplied by the lateral branch of the vagus nerve. They disappear during the metamorphosis, at least in the Anura, with the exception of _Xenopus_, in which they form conspicuous white objects. The white colour is caused by the tubes becoming choked with the débris of cells or coagulating mucous matter, so that it is doubtful if these organs, which moreover have sunk deeper into the skin, are still functional. In the terrestrial Urodela these organs undergo a periodical process of retrogression and rejuvenescence. During the life on land they shrink and withdraw from the surface, and their nerves likewise diminish, but in the breeding season, when the newts take again to aquatic life, they revive, are rebuilt and become prominent on the surface. They are an inheritance from the fishes, in which such lateral line organs are universally present.