COMPARATIVE ANATOMY: INTEGUMENT IN SCOLIODON AND RANA
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Scoliodon and Rana are poikilothermic animals. Scoliodon is an aquatic cartilage fish. Rana lives in water and on land-amphibian. In both the vertebrates the skin (integument) is the outermost covering of the body. It is multicellular and multilayered structure typically formed of an outer layer of 'epidermis' and an inner layer of 'dermis'. The integument provides a characteristic form to the body. It also protects the enclosed organs.
The epidermis is derived from the ectoderm and dermis from mesoderm of the embryo. The epidermis is multilayered and differentiated into stratified epithelium and cornification is not complete. The cells of stratum corneum are nucleated. The lowermost layer of the epidermis formed of living columnar cells and is called 'stratum malpighii'or stratlim germinativum.
|Scoliodon (Fish) - Skin||Rana (Frog) - Skin|
|1. Skin is rough & tough. It is firmly attached to the underlying muscles.||1. Skin is soft, smooth and loose. It is separated from the underlying muscles by lymph sacs.|
|2. The skin is divided into epidermis and dermis.||2. Same.|
|3. The epidermis is composed of many layers of similar epithelial cells. Stratum corneum is absent.||3. The epidermis is distinguished into stratum corneum and stratum malpighii.|
|4. Unicellular mucous glands are present in the dermis.||4. Mucous glands or cutaneous glands are multicellular and are present in the dermis.|
|5. Dermis is less vascularised.||5. Dermis is richly vascularised.|
|6. The skin is protective and sensory in function.||6. Skin is protective, sensory and respiratory (Cutaneous respiration) in function.|
|7. Placoid scales are present.||7. Scales are absent.|
|8. Dermis has no layers.||8. Dermis has stratum spongiosum & stratum compactum.|
|9. In the dermis chromatophore and iridocytes are present.||9. Chromatophores are found in the upper part of dermis. These help in changing the colour of integument.|
|10. In some deep-sea fishes light emiting photophores are present.||10. In some frogs (Bufo) poison glands are present near the tympanum.|