Editing Amphibian (section)

=== Skin ===
[[File:Tree frog congo.jpg|thumb|left|upright|alt=Common reed frog|The [[Aposematism|bright colours]] of the [[common reed frog]] (''Hyperolius viridiflavus'') are typical of a toxic species]]
The [[Wikt:integument|integumentary]] structure contains some typical characteristics common to terrestrial vertebrates, such as the presence of highly [[Keratin#Cornification|cornified]] outer layers, renewed periodically through a moulting process controlled by the [[pituitary gland|pituitary]] and [[thyroid]] glands. Local thickenings (often called warts) are common, such as those found on toads. The outside of the skin is shed periodically mostly in one piece, in contrast to mammals and birds where it is shed in flakes. Amphibians often eat the sloughed skin.<ref name="Collins" /> Caecilians are unique among amphibians in having mineralized dermal scales embedded in the [[dermis]] between the furrows in the skin. The similarity of these to the scales of bony fish is largely superficial. [[Squamata|Lizards]] and some frogs have somewhat similar [[osteoderm]]s forming bony deposits in the dermis, but this is an example of [[convergent evolution]] with similar structures having arisen independently in diverse vertebrate lineages.<ref>{{cite journal |author1=Zylberberg, Louise |author2=Wake, Marvalee H. |year=1990 |title=Structure of the scales of ''Dermophis'' and ''Microcaecilia'' (Amphibia: Gymnophiona), and a comparison to dermal ossifications of other vertebrates |journal=Journal of Morphology |volume=206 |issue=1 |pages=25–43 |doi=10.1002/jmor.1052060104 |pmid=29865751 |s2cid=46929507 |url=https://www.researchgate.net/publication/227806326 |access-date=November 10, 2016 |archive-date=December 16, 2017 |archive-url=https://web.archive.org/web/20171216161753/https://www.researchgate.net/publication/227806326 |url-status=live }}</ref>
[[File:FrogSkin.png|thumb|upright=1.35|Cross section of frog skin:
{{image key
|list type=ordered
|Mucous gland
|Chromatophore
|Granular poison gland
|[[Connective tissue]]
|[[Stratum corneum]]
|Transition zone
|[[Epidermis]]
|[[Dermis]]}}]]
Amphibian skin is permeable to water. Gas exchange can take place through the skin ([[cutaneous respiration]]) and this allows adult amphibians to respire without rising to the surface of water and to hibernate at the bottom of ponds.<ref name="Collins" /> To compensate for their thin and delicate skin, amphibians have evolved mucous glands, principally on their heads, backs and tails. The secretions produced by these help keep the skin moist. In addition, most species of amphibian have granular glands that secrete distasteful or poisonous substances. Some amphibian toxins can be lethal to humans while others have little effect.<ref name="amphibfacts">{{cite encyclopedia |url=http://www.eoearth.org/article/Amphibian_morphology_and_reproduction |title=Amphibian morphology and reproduction |date=October 12, 2008 |author1=Biodiversity Institute of Ontario |author2=Hebert, Paul D. N. |encyclopedia=Encyclopedia of Earth |access-date=August 15, 2012 |archive-date=February 1, 2008 |archive-url=https://web.archive.org/web/20080201074532/http://www.eoearth.org/article/Amphibian_morphology_and_reproduction |url-status=live }}</ref> The main poison-producing glands, the [[Parotoid gland|parotoids]], produce the neurotoxin [[bufotoxin]] and are located behind the ears of toads, along the backs of frogs, behind the eyes of salamanders and on the upper surface of caecilians.{{sfn | Stebbins | Cohen | 1995 | pp=10–11 }}

The skin colour of amphibians is produced by three layers of pigment cells called [[chromatophore]]s. These three cell layers consist of the melanophores (occupying the deepest layer), the guanophores (forming an intermediate layer and containing many granules, producing a blue-green colour) and the lipophores (yellow, the most superficial layer). The colour change displayed by many species is initiated by [[hormone]]s secreted by the pituitary gland. Unlike bony fish, there is no direct control of the pigment cells by the nervous system, and this results in the colour change taking place more slowly than happens in fish. A vividly coloured skin usually indicates that the species is toxic and is a warning sign to predators.<ref>{{cite book |title=The Integument: A Textbook of Skin Biology |last=Spearman |first=R. I. C. |year=1973 |publisher=Cambridge University Press |isbn=978-0-521-20048-6 |page=[https://archive.org/details/integumenttextbo00spea/page/81 81] |url=https://archive.org/details/integumenttextbo00spea |url-access=registration |quote=Amphibian skin colour. }}</ref>