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COMPARATIVE ANATOMY: INTEGUMENT IN REPTILES, BIRDS AND MAMMALS

Published in Zoology
Saturday, 08 July 2017 12:52
Comparison Of Integument Derivatives In Calottes (Reptile), Columba (Bird) And Oryctolagus (Mammal)

Calotes is a terrestrial Reptile (lizard). Columba is flying bird. Oryctolagus is a herbivorous mammal. All these animals are grouped under Amniota and columba & oryctolagus are warm blooded animals. The integument forms the outermost covering of the body in all these animals. It is multilayered in structure and is distinguished into epidermis and dermis. The epidermis consists of several rows of flattened stratified epithelial cells stratum corneum. Below this layer stratum Malpighi is formed with living columnar cells. The dermis is formed of connective tissue traversed with collagen and elastin fibres, muscles, nerves, blood capillaries and lymph vessels etc. It possesses an upper stratum spongiosum and a lower stratum compactum layers. The epidermis and dermis are formed from ectoderm & mesoderm layers.
 
CALOTES SKIN (REPTILE INTEGUMENT) COLUMBA SKIN (BIRD INTEGUMENT) ORYCTOLAGUS SKIN (MAMMAL INTEGUMENT)
1. In Calotes (Reptile) the skin is rough, thick, dry and scaly. Skin is suited to the terrestrial environment which prevents any loss of water. 1. In birds the Skin is thin, loose and dry. 1. In Mammals Skin is thick, elastic and water proof.
2. Epidermis has a heavily cornified stratum, corneum which produce into hormy epidermal scales. 2. The epidermis is thin and delicate all over the body except on sharks and feet where it is thick and produce epidermal scales. 2. The epidermal cells form into four layers - Stratum corneum, S. lucidum, S. granulo sum  & stratum.
3. The exoskeleton of scales is periodical­ly cast off either in fragments or as a sin' gle piece. In turtles & tortoises the epidermal bony plates are formed. In others the scales are modified into shields, scutes, spines etc. 3. The exo Keleton is in the form leathers which are formed from structure corneum & stratum malpighii. The feathers are keratinised. 3. The epidermis also forms Sebaceous and sweat glands. The mu­cous glands are ab­sent. The sweat glands help in excretion and maintain constant body temperature. Sebaceous glands se­crete 'sebum' which lu­bricates the skin and hairs. Hairs are present.
4. The glands are practically absent. The only glands present are 'scent glands'. 4. The epidermis is devoid of glands except the single "uropygial gland" present at the base of the tail. The oily secre¬tion of the glard is used for preening the leathers. 4. Presence of mammary glands is the charac­teristic of mammals (Rifled sebaceous glands.)
5. Dermis is thick having stratum spongiosum & stratum com pactum. 5. Two layers are present in the dermis which is thin. Vascular layer is present in between the two layers. 5. Dermis is very thick. It has intricate system of connective tissue fibres extending in all direc­tions.
6. Stratum spongiosum has numerous chromatophores. They exhibit   wide colour patterns. 6. Chromatophoresare absent. But the pigment is found in the feathers and scales. 6. Chromatophores are absent large dendritic melanophores are present.
7. Sensory corpuscles are absent. 7. Cutaneous receptors are present in the dermis. 7. Numerous tactile corpuscles are highly developed.
8. Fat cells are not present in the dermis. Femoral glands are present. 8. Fat cells are present in the dermis. 8. Subcutaneous layer is formed of adipose tissue (Fat cells).
9. Distal ends of the digits have nails or claws which formed from the homy epidermis. These grow  parallel to the surface of skin and formed of a dorsal plate 'unguis' (nailplate) and a ventral plate sub unguis (sole plate). 9. Similar claws are with unguis in the form of a long plate of keratin sharply curved and subunguis lies between its two edges. 9. Nails & hoofs are found. At the base of the nail, the epidermis is invaginated to form nailgroove and its part covering the nail root-eponychium.
10. Horny teeth are present which are acrodont or pleurodont Similar claws are with unguis in the form of a long plate of keratin. 10. Beaks are formed of enlarged epidermal scales which form hard keratinized covering over the jaw bones. 10. Hairs are keratin derivatives and exclusively present in mammals. These are strictly epidermal structures developed from stratum malpighii.
Bird Skin - Cross Section
Bird Skin - Cross Section

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