INTEGUMENT OF AMPHIBIA 



137 



from the niiderlyin^ tissues. The rich siij)])ly of lilood vessels which 

 extend into the coriuni faciUtate respiratory exchanges through the 

 skin, which in these forms may he the main respiratory organ. 

 Tlie gills of such forms as Xecturus are tuft-like ])rojections of skin 

 richly supplied by the capillaries of the corium. In such forms as 

 toads, which are primarily land-living forms, the epidermis is hard- 

 ened and thickened to prevent loss of moisture. 



The skin of the frog is surfaced with stratified squamous epithe- 

 lim, five to six rows of cells dee]). The basal cells are low columnar 











Fig. 83. — Photograph of integument of the frog with an epidermis composed of 

 stratified squamous epithelium and associated simple alveolar mucous glands. Im- 

 mediately below the epidermis there is a narrow region of loose vascular connective 

 tissue in which contracted chromatophores occur; below the gtands the corium is 

 composed of a dense fibrous tissue. 



or cuboidal, the intermediate cells flatten out toward the surface, 

 and the superficial scaly cells adhere to one another so as to form 

 a cuticular covering which sloughs off in sheet-like patches. Just 

 underneath the epithelium there is a loose vascular connective tissue 

 in which chromatophore cells are scattered, while beneath this is a 

 zone of more densely organized connective tissue. The deepest 

 region of the corium is densely organized, with ])arallel collagenous 

 bundles. Alveolar glands extend into the superficial corium beneath 

 the chromatophore network, each gland opening among the basal 

 cells of the epithelial covering. The excretory duct leading from 

 the mouth of the gland forms a channel passing through the epithe- 

 lium to the surface. 



