34 AMPHIBIA CHAP. 



paratively few vertical septa Ity whicli the upper and denser 

 layers, the corium proper, are connected with the underlyini^ 

 muscles. The spaces are filled with lymph, and into some of them 

 tlie ahnorinally expanded vocal sacs extend, notably in Pal lulicola, 

 Leptodactyl us, and other Cystignathidae, and in llliimuhrma. 



The cutis frequently forms papillae and prominent folds, 

 sometimes regular longitudinal keels on the sides of the back; Init 

 dermal, more or less calcified or ossified scales are restricted to 

 the Stegocephali and to the Apoda, q.r., y\). TO, ST. AVe con- 

 clude that the Urodela and Anura have entirely lost these organs. 

 Dermal ossifications, besides those which now form an integral 

 part of the skeleton, like many of the cranial membrane-bones, are 

 rare, and are restricted to the Anura. They are least infreijuent 

 on tlie head, where the skin is more or less involved in tlie 

 ossiiication of the underlying membrane-bones, for instance in 

 Triprion, Calyptocephalus, Hcmiphractus and Pelohates. The 

 thick ossifications in the skin of the back of several species of 

 Ceratophrys are very exceptional. In Brachycephalus ephijyjnuni 

 these dermal bones enter into connection with the vertebrae ; 

 small plates fuse with the dorsal processes of the first to tliird 

 vertebrae, while one large and thick plate fuses with the rest 

 of the dorsal vertebrae. Simple calcareous deposits in the 

 cutis are less uncommon, for instance, in old specimens of Bi'/o 

 vulgaris. We are scarcely justified in looking upon these various 

 calcifications and even ossifications as reminiscences of Stego- 

 cephalous conditions. 



The skin contains pigment. This is either diffuse or granular. 

 Diffuse pigment, mostly dark brown or yellow, occurs frequently 

 in the epidermis, even in the stratum corneum. The granular 

 pigment is stored up in cells, the chromatopliores, which send 

 out amceboid processes, and are restricted to the cutis, mostly 

 to its upper stratum, wliere they make their first appearance. 

 Contraction of the chromatopliores withdraws the pigment 

 from the surface, expansion distributes it more or less equally. 

 Tlie usual colours of the pigment are black, brown, yellow, and 

 red. Green and blue are merely subjective colours, due to 

 interference. A peculiar kind of colouring matter is the white 

 pigment, which probably consists of guanine, and is likewise 

 deposited within cells ; cf. the description of the white spots in 

 the skin of Hyla cocrulea. 



