AMPHIBIA. 



395 



is often rough, and the roughness is due in part to processes and ridges of 

 the corneous cells, in part to local thickenings of the epidermis itself. The 

 lower layers of the corium are loose in texture and contain lymph-spaces 

 continuous with the subcutaneous spaces so largely developed in this class. 

 Smooth muscle cells are found mixed with the fibrous tissue, and chro- 

 matophores or pigment cells in abundance. The colours of the pig- 

 ment are various, black, white, orange, metallic or iridescent : its state 

 of concentration in the cells depends on the activity of the nervous 

 system, and nerve fibres have been traced into direct continuity with the 

 cells. The glands are round or tubular. The former vary much in size ; 

 the small are scattered, the large are found chiefly on the head, neck and 

 flanks. Masses of them, known as ' Parotids,' are found on the neck in Bufo 

 and Salamandra. The tubular glands occur chiefly on the hand and foot, 

 and on the head in many tropical Salamanders. The gland-secretion is. 

 milk-white and poisonous. The young larva or tadpole of the Anura has 

 two collections of unicellular glands beneath the head. Their secretion is 

 sticky and serves to attach the larva to foreign objects. Variations from 

 the ordinary structure are seen in the development of epidermic nails in 

 the Japanese Salamander Onychodactylus and the ^Q^Dactylethra capensis. 

 Calcareous concretions are found in the dermis of the dorsum and dorsal 

 aspect of the limbs in the common Toad Bufo vulgaris and B.japonicus. 

 Bony dorsal plates are developed in certain species of Ceratophrys and 

 Ephippifer ^Brachycephalus) among Anura. The Gymnophiona (Caecilia 

 and its allies) have semicircular cutaneous lamellae in which are imbedded, 

 except in Siphonops annulatus, cycloid dermal scales containing calcareous 

 concretions. This dermal skeleton is well developed and ossified in the 

 extinct Stegocephali ( = Labyrinthdontia, &c.). It generally consists of a 

 median anterior thoracic plate, rhomboidal in shape, with the addition of 

 two antero-lateral pieces in some instances, and of a series of ventral 

 scales usually arranged in oblique lines which meet one another ventrally 

 at an angle pointing forwards. These scales, as a rule, only cover the 

 abdominal surface. Sometimes, however, the back, tail and limbs are also 

 protected, but by scales which differ much in shape, &c., from the ventral, 

 e. g. in the Hylonomidae. The organs of the lateral line are not known to 

 exist in any Gymnophiona, except the larval Epicrium glutinosum, but are 

 found in the larvae of every other order. They are persistent in all Urodeht 

 which lead an aquatic life, e.g. Proteus, Triton, but are lost in those which 

 are terrestrial when adult, e.g. Salamandra, as well as in all adult Anura. 

 On the head it is generally possible to distinguish the supra- and infra- 

 orbital lines of organs : the mandibular is generally broken up into an 

 anterior and a posterior part, and the commissure across the supra- 

 occipital region occurs only in Menopoma. But in some instances the 

 number of organs is great, and it is difficult to trace the typical arrangement. 



