The main function of the integument of vertebrates is to separate and protect the organism from the environment. Present-day vertebrates display profound alterations of the skin related to protection which have developed during a long history of evolution. Modifications of the epidermis that is in direct contact with the environment have been essential to maintain stability of the interior milieu in water, in the air and on land, and to provide protection against the perils of the environment. Development of keratinized epidermal appendages, such as cornified “teeth” in lampreys and breeding tubercles in fishes; scales, claws and shell of reptiles; scales, claws, beak and feathers of ayes; and scales, claws, hooves, nails, quills, wool, hairs and horns of mammals, have been indispensible not only for protective purposes but also for mating behavior, locomotion, predation, homoiothermy etc. Evolution of these keratinized structures has been extensively studied by classical histological methods, but the concepts are speculative rather than factual, including development of feathers from scales and hairs from interscale epidermis (Spearman 1964). Evolution of epidermal appendages is not yet understood.
KeywordsPermeability Polypeptide Macromolecule Dermatol Protec
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