ii SKIN 33 



the digging spur or spade of Peldbates. 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 temporaries nearly the whole surface of the body 

 becomes covered with rosy papillae during the breeding season. 

 Similar nuptial excrescences are common, and are most note- 

 worthy 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 debris 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 rejuven- 

 escence. 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. 



The cutis of most Amphibia is very rich in lymph -spaces, 

 which, especially in the Anura, assume enormous proportions, 

 since the so-called subcutaneous connective tissue forms com- 



VOL. VIII D 



