Digestive System Of Bird: Eg: Pegion Digestive System (Columba)

Digestive System Of Mammal: Eg: Rabbit Digestive System (Oryctolagus)

Digestive System Of Reptile: Eg: Lizard Digestive System (Calotes)

In previous topic we discussed about the comparative anatomy of digestive system of frog and shark. In this topic we discussed about the comparative anatomy of digestive system of Bird, Mammal and Reptiles.
Calotes is a poikilothermic and terrestrial lizard. Columba and Oryctolagus are warm blooded animals. Columba is adapted for mode of life-bird. Oryctolagus (Rabbit) is a mammal. The digestive system consists of alimentary canal and its associated digestive glands. The living of the alimentary canal is mostly endodermal in origin being derived from the wall of the archenteron. Distinc' salivary glands secreting enzymes are present only in mammals. In reptiles, the oral glands are present in various positions termed labial, parotid, lingual & sublingual etc. The secretions of which serve primarily to keep the mouth moist and secondarily to facilitate the movements of the tongue. The other connected with the midgut and arising as out growth are the liver and pancreas.
digestive system bird thumb23
Calotes (Lizard) Columba (Pigeon) Oryctoiagus (Rabbit)
1. Mouth is a wide, slit present at the anterior end of head. 1. Mouth is terminal, slitlike aperture bounded by horny Jaws. 1. Mouth is sub-terminal, cleft bounded bv mobile, fleshy lips.
2. Buccal cavity is a narrow gap. Labial glands are present on lips.They secrete mucous. 2. Buccal cavity is narrow and some what and dorsoventrally flattened. 2. Buccal cavity is a spacious chamber andits space between lips and the teeth is called vestibule. This receives the mouth opening.
3. On both jaws teet are present, polyphyodont homodont teeth arranged in a single row on each jaw. Teeth are not useful for mastication. Pleurodont dentition is present. 3. Jaws are modified into tooth less beak. 3. Dentition in mammals:Teeth are diphyodont, heterodont and thecodont. These are arranged in a single row on each Jaw.Teeth are modified cutting (Incissors) and chewing (Premolars & molars) canines are absent in rabbit.
4. Tongue is attached posteriorly  to the floor of buccal cavity and is free anteriorly. Sensory papillae are present. 4. Tongue is narrow triangular and fleshy. Its surface is covered with horny material and bears thorn-like projections which carry taste buds and mucous glands. 4. Tongue is highly specialized, fleshy and muscular and can be moved in different directions. It can be protruded out. Its surface is rugose being covered with numerous papillae along with taste buds.
5. A pair of internal nostrils open into the roof of the buccal cavity anteriorly. Hard palate is present. 5. A bony palate is wanting in birds but a pair of palatal folds and palatal groove between the two folds are present. Internal nostrils are located dorsal to the palatal folds. 5. The nasal passages are separated from the buccal cavity by a bony palate. The internal nostrils open into the pharynx nearer to glottis.
6. A bony palate is present covering the roof of the buccal cavity. 6. A bony palate is absent. But soft palate is formed of two membranous folds. 6. The palate is differentiated into anterior bony hard palate and a soft palate is formed of connective tissue. The soft palate is produced behind into a process – velum palati hanging down from the roof, which prevents the entry of food into nasal passage.
7. Unicellular mucous glands are present and keep the buccal cavity always wet. 7. Unicellular mucous glands are absent in the epithelium of bucco-pharyngeal region. 7. Unicellular mucous glands are absent. But multi cellular serous glands are present.
8. Salivary glands are absent. But labial glands are open at the lips which do not play any role in digestion. 8. Salivary glands which open into the buccal cavity are lingual, mandibular, maxillary, cricoary tenoid, palatinal and sphenopalatinal glands. 8. The multi cellular salaivary glands are four pairs. They are Infra orbital, parotid, sublingual and sub-maxillary glands. Palatine, tonsillar, superior & inferior labial glands are also associated.
9. Pharynx is marked off. On the roof of pharynx near the junction of two jaws a pair of openings is called Eustachian apertures. The floor of pharynx has the glottis. 9. Pharynx is marked off from the buccal cavity but it receives, internal nostrils through which nasal passages open into its cavity, the gullet & glottis. 9. Pharynx is not sharply demarcated from the buccal cavity. It receives the openings of esophagus and the glottis.
10. Esophagus is a narrow tube and straight extends through the neck. Mucous glands are present. 10. Oesophagus is a bng and narrow tube. It has thick walls. Mucous glands are absent. 10. Oesophagus is a long thin walled tube. It is clearly marked off from the pharynx as well as stomach. Mucous glands are present.
11. Crop is absent. 11. The oesophagus is dilated into a thin-walled sac the crop. It secrete pigeon milk in both sexes and used to feed the young birds. 11. Crop is absent. The wall of oesophagus is produced into the cardiac stomach to form cardiac valve.
12. Stomach is a sac- like structure. Its anterior part is cardiac stomach and posterior part is pyloric stomach. At the end of pyloric stomach a small constriction is present. It possesses a pyloric sphincter. 12. Stomach is divided into a glandular proventriculus and posterior muscular gizzard. Gizzard acts like grinding apparatus. Pyloric valve absent. 12. Stomach is divisible into cardiac, fundic and pyloric parts. Pyloric stomach contains pyloric valve.
  13. Intestine is differentiated into duodenum and ileum. Intestine very long and very much coiled because is a herbivorous animal 13. Same structures are present. But the bile duct and pancreatic ducts open separately into the proximal and distal ends of the duodenum respectively.
 14. A single rectal caecum is present. 14. At the junction of ileum & colon, two divertulae are present. These are called Rectaicaeca. 14. An ilio-colic valve is present at the junction of the small intestine and large intestine or colon. At the junction of these portions, a spiral shaped vermi form appendix is present. At the regular intervals of the colon shows pocket-like pouches - 'Haustra'.Colon shows longitudinal muscle folds taeniae'. Cellulose enzyme is produced.
15. Cloaca is common opening for digestive'and urinogenital ducts. It is divided into coprodaeum, urodaeum, and proctodaeum. 15. Cloaca is large and divided into the same parts. On the dorsal side of the proctodaeum a thick walled blindsa "Bursa fabricii" is present. It becomes degenerated in the adult and is known as cloacal thymus. 15. Cloaca is absent. Anus is present.
16. Liver is bilobed gland. The right lobe has a gall bladder. It secretes bile (alkaline& no enzymes). 16. Liver is bilobed dark red gland. Gall Bladder is absent. Separate bile ducts are formed.Liver secretes bile. 16. Liver is very large and consists of five lobes. Kupffer's cells are present in the liver. Liver secretes bile. Gall Bladder is present.
17. Pancreas is a whitish gland present between stomach duodenum. 17. Pancreas is a pink coloured gland present the loop of duodenum. Three pancre catic ducts open into the duodenum. 17. pancreas is a diffused gland of pink colour. Pancreatic duct opens into the duodenum.
18. Gastric, intestinal glands are also present. 18. Same are present. 18. Same are present.
digestivesystemrabbitmammal thumb17
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.
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

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.


Written by Saturday, 08 July 2017 00:17
Herdmania is a bisexual animal. It is a protogynous animal. Ovary matures’ first. Hence cross fertilization takes place.
Herdmania contains a pair of gonads. The left gonad lies in the intestinal loop above the heart. Each gonad shows 10 to 25 lobes arranged in two rows. The median lobe is single and large. Other lobes are oval in shape.
Each lobe shows outer large testicular part and inner small ovarian part. The testicular part is brick red in colour and produces sperms. The ovarian part is pink in colour and produce ova. From each testicular part sperm ductule will arise. They open into spermduct. From each ovarian part ovarian ductule will come. They open into the oviduct. Each gonad has an oviduct and spermduct. They run parallelly and open separately into cloaca behind anus.


Written by Saturday, 08 July 2017 00:03
Herdmania is a hermaphrodite animal. The fertilised eggs undergo holoblastic unequal clevage and it develops into blastula. it shows upper micromeres and lower macromeres. By invagination of the macromeres gastrulation takes place and gastrula is formed. This gastrula develops into a tailed larva called Ascidian Tadpole larva. (Herdmanis life history, is not clearly known. Clavilina’s life history is known. It is followed here.
The larva is 3 mm in length. It has short oval body and a long tail.
This larva shows all the chordate features.
  1. The body is covered by thin test.
  2. The tail is long and shows a tail fin or caudal fin.
  3. The tail is supported by notochord. Hence it comes under urochordata.
  4. On the dorsal side above the notochord hollow nerve cord is present. This nerve cord is enlarged at the anterior end as a cerebral vesicle. In the cerebral vesicle pigmented eye spot is present. Statocyst is also present. They work as sense organs.
  5. On either side of the notochord in the tail region muscles are Present which are helpful in the locomotion.
  6. On the trunk region digestive system is present. It shows large pharynx with few gills slits. They open into atrium. On the mid ventral floor of the pharynx an endostyle is present.
  7. Atrium opens out through atriopore.
  8. Below the pharynx on the ventral side a muscular heart is present.
  9. On the anterior end of the trunk three adhesive papillae are present These are very much useful to attach the larva to the substratum.
This Herdmania tadpole larva shows all chordate characters. This larvae ‘undergoes retrogressive’ metamorphosis and develops into adult Herdmania.


Written by Friday, 07 July 2017 19:47
During metamorphosis the larva will loose all the chordate characters and attains an invertebrate like form. This type of metamorphosis, where highly advanced larval form ends in a lowly organised adult is called retrogressive metamorphosis.
Fixation of the larva: The larva swims for some time without feeding. It is fixed to a sub-stratum with the help of the adhesive papillae. It stands erect with the tail upwards. Then it undergoes retrogressive metamorphosis.
Changes during Metamorphosis:
  1. Notochord, nerve cord muscles and tail will be reduced. All the above structures will help the larva to swim freely in the water. But they are not useful to the sedentary adult.
  2. The alimentary canal becomes complicated. The pharynx en larges in size. The number of gill slits will increase by divisions. The stomach and intestine will grow.
  3. The nervous system is reduced and the anterior part of nervous system is developed into a small neuralganglion attached to it neural gland is present.
  4. The atrial cavity enlarges into a sac like structure.
  5. The eyespot and statocyst will completely disappear.
  6. Gonads develop from mesencyme.
When these changes are taking place, the region between the adhesive papillae and mouth grows very rapidly. At the same time the growth of the dorsal region is stopped. Because of this, the body rotates through 180° angle and mouth is brought to the top.


Written by Friday, 07 July 2017 19:32
In the test of Herdmania two types of calcareous spicules are Present. They are:
  1. Microscleres: These are 40 to 80 microns in length. They are minute.
  2. Megascleres: These are long spicules. They show different shapes. They are 1.5 to 3.5 mm in length. They are two types.
    a) Spindle shaped Megascleres. They are 1.5 to 2.5 mm in length.
    b) Pipette shaped Megascleres. They are 3.5 mm in length.
The microscleres are present only in the test. But the megascleres occur in the test, body wall, and viscera.
  1. They give support to the test.
  2. They protect the animal from predators.
  3. They fix mantle with test.


Written by Friday, 07 July 2017 18:44
A neural gland is present above the brain in herdmaina. It is brown in colour. It is present in the mantle. It is 4mm in diameter. It show branching tibuIes. At one end it leads into a short duct which opens by ciliated funnel above the dorsal tubercle. In the blood nephrocytes cell are present. They coiled waste matter. They come to the neural gland from there, they are sent out The neural gland secretes a hormone. It help in metamorphosis. Neural gland is considered homologous to pituitary glands of vertebrates.


Written by Friday, 07 July 2017 18:29
Herdmania shows brain or nerve ganglion. It is 4 mm long. It is present in the mantle in between the two siphons. A neural gland is present above the brain. From the brain three nerves arise, one goes to the bronchial siphon, and two will go to the atrial siphon. The brain represents the degenerated nervous system of the larva.
  1. Red pigmented spots on the test are photoreceptors. They are sensitive to light.
  2. Sensory cells of the margins of siphons and tentacles are tango receptors. They are sensitive to touch.
  3. The cells on the margins of siphons are rheo receptors. They are sensitive to water currents.
  4. Cells lining the siphons are thermo receptors. They are sensitive to changes of temperature.


Written by Friday, 07 July 2017 18:09
Herdmania is a simple ascidian, In Indian ocean this genus is represented by 4 species.
1. Herdmania pallida 2. H. ennurensis 3. H. mauritiana 4. H. ceylonica
Herdmania belongs to,
  • Phylum: Chordata
  • Sub-phylum: Urochordata
  • Class: Ascidiacea
  • Order: Pleurogona
Herdmania is a marine and sedentary animal. It is fixed to rocky substratum by a flat base. When it is disturbed, it suddenly contracts its body, and emits inner contents with force through its apertures. Hence it is called Sea squirt.
External Features:
It is potato like in shape. It is pink in colour. On the free side, body shows two projections, the brançhial and atrial siphons. The branchial siphon is short. The branchial siphon shows a branchial aperture or the mouth. The atrial siphon is longer. It bears the atrial aperture. Both the openings are bounded by four lips.
Herdmania - External Characters:
Test of Herdmania:The body of this animal is covered and protected by test. It is a thick, leathery covering of the body. It is secreted by the epidermis of the body wall. It has matrix, corpuscles, fibrils, blood vessels and spicules.
The matrix is composed of tunicin, which is cellulose. The cells in the test are of six types, large eosinophilous cells, amoeboid cells, small eosinophilous cells, vacuolated cells, receptor cells and nerve cells.
Fine fibrils present in the matrix. In the test blood vessels are present. In the test the spicules are calcareous spicules. They are microscleres, and megascleres.
Herdmania test thumb13
The test protects the body. Anchors the animals to substratum. Its spicules form a supporting frame work.
Herdmania Body Wall:
The body-wall of Herdmania is called Mantle. It is thick, and muscular in the antero-dorsal region of the body. It is thin, non-muscular and transparent in the postero ventral region. It shows epidermis, mesenchyme, and inner epidermis.
1. Epidermis: It Is single layer of cells. It covers the bronchial and atrial apertures and siphons. The epidermis is interrupted at places where spicules and blood-vessels pass from the mantle into the test.
2. Mesenchyme: It develops from the mesoderm. It has connective tissue containing blood-sinuses, muscle-fibers, nerve fibers and cells. The muscle fibers are long and flat. They contain large nuclei.
Herdmania Body wall thumb23
3. Inner Epidermis: It is single layer of flat cells. It forms the lining of the atrial cavity.
  1. The body-wall protects visceral organs.
  2. The outer epidermis secretes the test.
  3. The musculature brings contraction of the body and the siphons.
Herdmania Atrium:
In Herdmania coelome is not developed. Atrium is a spacious ectoderm lined cavity. it is covered by the mantle A part of the atrium surrounds the pharynx. The stigmata of the pharynx open into this cavity. Part of the atrium is dorsal to the pharynx. It is very wide and is called cloaca. The rectum and gonoducts open into this. The cloaca opens to the exterior through atrial siphon and trial aperture. The atrial siphon shows a ring of processes called atrial tentacles at its base.

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