Animal Tissues PDF

ANIMAL TISSUES A group of cells having same origin, structure and function are called the tissues. Animal tissues are 4 types: (i) Epithelial (ii) Connective (iii) Muscular (iv) Neural I. EPITHELIAL TISSUE (EPITHELIUM) It has a free surface that faces body fluid or outside environment. C...

ANIMAL TISSUES A group of cells having same origin, structure and function are called the tissues. Animal tissues are 4 types: (i) Epithelial (ii) Connective (iii) Muscular (iv) Neural I. EPITHELIAL TISSUE (EPITHELIUM) It has a free surface that faces body fluid or outside environment. Covers or lines body or body parts. Compactly packed cells with little intercellular matrix. (a) Unicellular (b) Multicellular Epithelial tissues are 2 types: Simple and Compound. Based on mode of pouring of secretions, glands are 2 types: Exocrine glands: Here, secretions are released through 1. Simple epithelium ducts (tubes). Exocrine glands secrete mucus, saliva, It is composed of a single layer of cells. It lines body cavities, earwax, oil, milk, digestive enzymes etc. ducts and tubes. Based on structural modification of cells, Endocrine glands: Ductless. They produce hormones. simple epithelium is 3 types: 2. Compound epithelium o Squamous epithelium: Made up of more than - Thin layer of flattened cells with irregular boundaries. one layer (multi- - Found in the walls of blood vessels and lung alveoli. layered) of cells. - Functions: Form a diffusion boundary. Limited role in o Cuboidal (cubical) epithelium: secretion & absorption. - Composed of cube-like cells. They cover dry surface - Found in ducts of glands and tubular parts of nephrons. of skin, moist surface of buccal cavity, pharynx, inner - Functions: Secretion and absorption. lining of ducts of salivary glands and pancreatic ducts. - The epithelium of proximal convoluted tubule (PCT) Function: Protect against chemical & mechanical stresses. of nephron in the kidney has microvilli. Cell junctions: The junctions that provide structural and o Columnar epithelium: functional links between adjacent cells. They are found in - Composed of tall and slender cells. epithelium and other tissues. They are 3 types: - Their nuclei are located at the base. i. Tight junctions: Help to stop substances from leaking - Free surface may have microvilli. across a tissue. - Found in the lining of stomach and intestine. ii. Adhering junctions: Perform cementing to keep - Functions: Secretion and absorption. neighbouring cells together. iii. Gap junctions: Facilitate communication b/w adjoining cells by connecting the cytoplasm for rapid transfer of ions, small molecules and sometimes big molecules. II. CONNECTIVE TISSUE It links and supports other tissues/organs. They are most abundant in complex animals. All connective tissues except blood have fibroblast cells. They secrete structural fibrous proteins called collagen & Modification of columnar or cuboidal cells elastin. They give strength, elasticity & flexibility to tissue. The cells also secrete modified polysaccharides (matrix), Ciliated epithelium: which accumulate between cells and fibres. - Cells bearing cilia on their free surface. Types of connective tissues: Loose, Dense & Specialised. - Present in the inner surface of hollow organs like bronchioles and fallopian tubes. 1. Loose Connective Tissues - Functions: To move particles or mucus in a specific In this, cells (fibroblasts, macrophages, mast cells etc.) and direction over the epithelium. fibres are loosely arranged in a semi-fluid matrix. Glandular epithelium: For secretion. They are 2 types: It is 2 types: Areolar & Adipose. Unicellular: Consists of isolated glandular cells. o Areolar tissue: E.g. Goblet cells of the alimentary canal. - Present beneath the skin. Multicellular: Contains cluster of cells. E.g. salivary - It serves as a support framework for epithelium. glands. 1  Limb bones serve weight-bearing functions. Take part in locomotion and movements. Blood cells are produced in bone marrow. Blood: o A fluid connective tissue containing plasma, red blood cells (RBC), white blood cells (WBC) and platelets. o Helps in the circulation of various substances. o Adipose tissue: III. MUSCLE TISSUE - Seen mainly under skin. - The tissues made of many muscle fibres (muscle cells). - Its cells (adipocytes) store fats. - Muscle fibres are composed of numerous fine myofibrils. - Excess nutrients which are - Muscle fibres can contract (shorten) and relax (lengthen). converted into fats are stored in - Muscles take part in locomotion and movements. this tissue. - Muscles are 3 types: skeletal, smooth and cardiac. 2. Dense Connective Tissues In this, fibres and fibroblasts are compactly packed. 2 types: o Dense regular connective tissues: - Show regular pattern of fibres. - Collagen fibres are present in rows between many parallel bundles of fibres. - E.g. tendons & ligaments. 1. Skeletal (striated or voluntary) muscle i. Tendons: Attach - They are attached to bones. E.g. Biceps. muscles to bones. - Striations are present in muscle fibres. ii. Ligaments: Attach one bone to another. - Muscle fibres are bundled together in a parallel fashion. o Dense irregular connective tissues: - A sheath of tough connective tissue encloses several bundles of muscle fibres. Irregular pattern of fibres. - Fibroblasts & fibres (mostly 2. Smooth (non-striated or visceral) muscle collagen) are oriented - Involuntary and fusiform (Fibres taper at both ends). differently. - No striations. - This tissue is present in skin. - Cell junctions hold them together and they are bundled together in a connective tissue sheath. - They are seen in the wall of internal organs such as the 3. Specialized Connective Tissues blood vessels, stomach and intestine. Cartilage: 3. Cardiac muscle o In this, intercellular material - Involuntary muscle seen only in the heart. (matrix) is solid and pliable - Cell junctions fuse the plasma membranes of cardiac (due to chondroitin salts) muscle cells and make them stick together. and resists compression. - Communication (gap) junctions (intercalated discs) at o Cartilage cells (chondrocytes) are enclosed in small some fusion points allow cells to contract as a unit, i.e., when cavities within the matrix secreted by them. a cell receives signal to contract, other cells also contract. o Most of the cartilages in vertebrate embryos are replaced by bones in adults. IV. NEURAL TISSUE o Cartilage is present in the tip of nose, outer ear, joints Made up of neurons (unit of neural system). in the vertebral column, limbs and hands in adults. Responsible for control and co-ordination of the body. Bone: Neurons are excitable cells. They carry impulses. o It has hard and non-pliable Neurons are protected and supported by neuroglial cells. matrix rich in calcium salts Neuroglia make up more than half the volume of neural tissue. and collagen fibres which ORGAN AND ORGAN SYSTEM give bone its strength. Cells → tissues → organs → organ systems. o Bone cells (osteocytes) are seen in spaces called lacunae. This organization is essential for better coordinated o Functions: It provides structural frame to the body. activities of cells. Support and protect softer tissues and organs. An organ is made of one or more type of tissues. E.g. Heart has epithelial, connective, muscular & neural tissues. 2  MORPHOLOGY & ANATOMY OF COCKROACH Morphology: Study of external features of organisms. o Forewings (mesothoracic) or tegmina: Opaque, dark Anatomy: Study of morphology of internal organs. and leathery and cover the hind wings when at rest. Cockroach (Periplaneta americana) are nocturnal, o Hind wings (metathoracic): Transparent, membranous omnivores and live in damp places. and are used in flight. Colour: Brown or black. Bright yellow, red & green Abdomen coloured cockroaches are also seen in tropical regions. It consists of 10 segments. Size: ¼ inches to 3 inches (0.6-7.6 cm). In females, 7th (boat shaped), 8th & 9th sterna form a brood Systematic position (genital) pouch. It contains female gonopore, Phylum : Arthropoda spermathecal pores & collateral glands. Class : Insecta In males, genital pouch lies at the hind end of abdomen Genus : Periplaneta bounded dorsally by 9th & 10th terga and ventrally by the Species : americana 9th sternum. It contains dorsal anus, ventral male genital pore (gonopore) and gonapophysis. MORPHOLOGY OF COCKROACH In both sexes, 10th segment bears a pair of jointed anal The adults are about 34-53 mm long. cerci. Males bear a pair of short, threadlike anal styles. Body is covered by a hard brown chitinous exoskeleton. Differences between male & female cockroaches In each segment, exoskeleton has hardened plates called Male Female sclerites (dorsal tergites & ventral sternites). They are i. Larger size Smaller joined to each other by a thin and flexible articular ii. Wings extend beyond the Wings do not extend beyond membrane (arthrodial membrane). tip of the abdomen. the tip of abdomen. The body has 3 regions – head, thorax and abdomen. iii. Narrow abdomen Broad abdomen iv. Anal styles present Absent v. Brood pouch absent Present ANATOMY OF COCKROACH Digestive system Alimentary canal has 3 parts: foregut, mid gut & hindgut. Foregut: It is lined by cuticle. It includes Head Mouth → pharynx Triangular head is formed by 6 fused segments. → oesophagus → It shows great mobility in all directions due to flexible neck. crop (to store food) Head bears a pair of thread-like antennae, a pair of → gizzard compound eyes and biting & chewing type mouth parts. (proventriculus). Gizzard helps in grinding the food. It has an outer layer of thick circular muscles and thick inner cuticle forming 6 chitinous plates (teeth). Mid gut (Mesenteron): It is not lined by cuticle. 6-8 tubules (hepatic or gastric caecae) are seen at the junction of foregut & mid gut. They secrete digestive juice. At the junction of mid gut & hindgut, there are 100-150 yellow coloured thin filamentous Malpighian tubules. Mouthparts: a labrum (upper lip), 2 mandibles, 2 Hindgut: It is broader than mid gut and lined internally by maxillae, hypopharynx (tongue) & a labium (lower lip). cuticle. Hindgut includes ileum, colon & rectum. Rectum opens out through anus. Thorax It has 3 parts: prothorax, mesothorax & metathorax. Circulatory system The head is connected to thorax by a neck (short extension - Blood vascular system: open type. of the prothorax). - Blood vessels are poorly developed and open into space Each thoracic segment bears a pair of walking legs. (haemocoel). 2 pairs of wings: Forewings (2) and Hind wings (2). 3 - Visceral organs located in the Each testis → a thin vas deferens → seminal vesicle → haemocoel are bathed in blood ejaculatory duct → male gonopore. (haemolymph). - Haemolymph= colourless plasma + haemocytes. - Heart consists of elongated muscular tube lying along mid dorsal line of thorax and abdomen. - It has funnel-shaped chambers with ostia on either side. - Blood from sinuses enter heart through ostia and is pumped Seminal vesicles: To store sperms. Sperms are glued anteriorly to sinuses again. together to form bundles called spermatophores. They are Respiratory system discharged during copulation. Accessory glands: Include a mushroom gland (in 6th-7th - It consists of a network of trachea that open through 10 abdominal segments) and phallic gland. Their secretions pairs of small holes called spiracles present on the lateral nourish the sperms. side of the body. External genitalia (male gonapophysis or phallomeres): - The thin branches of tracheal tubes are called tracheoles. Chitinous asymmetrical structures, surrounding the male They carry oxygen from the air to all parts. gonopore. - The opening of the spiracles is regulated by sphincters. - Gas exchange takes place at the tracheoles by diffusion. Female reproductive system: Excretory system - Uricotelic. Excretory organ is Malpighian tubules. - Each tubule is lined by glandular and ciliated cells. They absorb nitrogenous wastes and convert them into uric acid which is excreted out through the hindgut. - Fat body, nephrocytes & urecose glands also help in excretion. Nervous system - It consists of segmentally arranged ganglia joined by It consists of 2 large ovaries, oviducts, spermatheca, paired longitudinal connectives on the ventral side. genital chamber, Colleterial glands etc. - 3 ganglia lie in the thorax and 6 in the abdomen. Ovaries lie laterally in the 2nd – 6th abdominal segments. - The head holds only a bit of nervous system. Remaining Each ovary is formed of 8 ovarian tubules (ovarioles), part is situated along the ventral part of the body. So, if the containing a chain of developing ova. head of cockroach is cut off, it will still live for one week. Oviducts of each ovary unite into a single median oviduct - The supra-oesophageal ganglion (brain) supplies nerves (vagina) which opens into the genital chamber. to antennae and compound eyes. A pair of spermatheca is present in the 6th segment which - Sense organs: Antennae, eyes, maxillary palps, labial opens into the genital chamber. palps, anal cerci etc. - Sensory receptors of antennae monitor the environment. Sperms are transferred through spermatophores. Their fertilised eggs are encased in oothecae. - Each compound eye consists of about 2000 hexagonal Ootheca is dark reddish to blackish brown capsule, 8 mm ommatidia. Using these, a cockroach can receive several long. Females lay 9-10 oothecae, each contain 14-16 eggs. images of an object. This is called mosaic vision. It has - Development of P. americana is paurometabolous, more sensitivity but less resolution, being common during (development through nymphal stage). night (hence called nocturnal vision). - Nymphs look like adults. They moult 13 times to reach the Reproductive system adult form. The next to last nymphal stage has wing pads. Cockroaches are dioecious. Only adult cockroaches have wings. Male reproductive system: ECONOMIC IMPORTANCE OF COCKROACH It consists of a pair of testes, seminal vesicles, accessory They are pests because they destroy food and contaminate it glands & external genitalia. Testes: Lie laterally in the 4th -6th abdominal segments. with their smelly excreta. They also transmit bacterial diseases like cholera, typhoid, tuberculosis etc. 4  MODEL QUESTIONS 1. Find the relationship between first two words and suggest a suitable word in the fourth position. a. Squamous epithelium: lining of blood vessels Cuboidal epithelium: ……………………. b. Cartilage: chondrocytes Bone: …………………. c. Frog: Kidney Cockroach: ……………….. 2. Odd man out. Justify your answer. a. Areolar tissue, blood, neuron, tendon Mushroom gland, Ommatidium, Ootheca, Oviducts b. Maxilla, Mandible, Labrum, Antennae d. Exocrine, Endocrine, Salivary gland, Ligament 3. Identify the following tissues and write down their location. a. Tissue which store fat c. Tissue that connects muscle and bone b. Tissue that conducts impulses d. Tissue that serves as supporting frame of body 4. Identify the following tissue and label A, B, C & D. c. 5. Two types of muscle tissues are diagrammatically represented. A B a. Identify muscle tissues A and B. Mention their location. b. Find out any two differences between them. 6. Prepare a flowchart using the following terms. Crop, Pharynx, Ileum, Mouth, Oesophagus, Mesenteron, Anus, Gizzard, Colon 7. Observe the diagram given below: a. Identify the figure. b. Label the parts P, Q, R and S. 8. Analyse the following statements. Find out the wrong statements and rewrite them correctly. a. In cockroach, hepatic or gastric caecae act as the digestive glands. b. Mushroom gland and phallic gland are concerned with female reproductive system of cockroach. c. Antennae, eyes, maxillary palps, labial palps etc. are the sensory organs of cockroach. d. Anal cerci are the structures present only male cockroach and used to identify the sex of cockroach. 5  MORPHOLOGY & ANATOMY OF EARTHWORM Systematic position - Epidermis: Made up of a single layer of columnar epithelial cells which contain secretory gland cells. Phylum : Annelida - Two muscle layers (circular and longitudinal). Class : Oligochaeta - An innermost coelomic epithelium. Genus : Pheretima Species : posthuma Digestive system Earthworm is a reddish-brown terrestrial invertebrate that inhabits the upper layer of moist soil. During day time, they live in burrows made by boring and swallowing the soil. Common Indian earthworms: Pheretima and Lumbricus. MORPHOLOGY OF EARTHWORM Earthworms have long segmented cylindrical body. - The straight alimentary canal extends from first to last Number of segments (metameres): about 100-120. segment of the body. It has Dorsal surface has a dark median mid dorsal line (dorsal - Mouth → buccal cavity (1-3 segments) → muscular blood vessel) along the longitudinal axis of the body. pharynx (4th segment) → oesophagus (5-7 segments) → First segment (peristomium or buccal segment) bears the muscular gizzard (8-9 segments) → stomach (9-14 mouth. A lobe called prostomium covers the mouth. segments) → Intestine (15th segment to last) → anus. Prostomium is sensory in function and is used to force open - Gizzard helps to grind soil particles, decaying leaves, etc. cracks in the soil into which the earthworm may crawl. - Calciferous glands, present in the stomach, neutralise the In a mature worm, segments 14-16 are covered by a dark humic acid present in humus. band of glandular tissue called clitellum. - A pair of short and conical intestinal caecae project from Body has 3 regions: preclitellar, clitellar & postclitellar. the intestine on the 26th segment. 4 pairs of spermathecal apertures are found on ventro- - The intestinal part between 26-35 segments has an internal lateral sides of intersegmental grooves (5th -9th segments). median fold of dorsal wall called typhlosole. It increases A single female genital pore is present in the mid-ventral area of absorption. line of 14th segment. - The organic rich soil is digested in the digestive tract by A pair of male genital pores is present on the ventro - lateral digestive enzymes. Digested nutrients are absorbed sides of the 18th segment. through intestinal membranes. Their faecal deposits are Many minute nephridiopores open on the body surface. known as worm castings. All segments except the first, last and clitellum bear S- shaped setae, embedded in the epidermal pits. Setae can be Circulatory system (blood vascular system) extended or retracted. Their function is locomotion. ANATOMY OF EARTHWORM Body wall It is composed of - Outermost thin non-cellular cuticle. 6 - Circulatory system is closed type (blood flows through Testes: 2 pairs. Enclosed in testis sacs in 10th & 11th heart and blood vessels). segments. The sperms from testes shed into testis sacs. From - Consists of blood vessels, capillaries and heart. where, they enter seminal vesicles for maturation. Mature - Contractions keep blood circulating in one direction. sperms move back into testis sacs and enter spermiducal - Blood glands are present on the 4th, 5th & 6th segments. funnels which are connected to vasa deferentia (spermatic They produce phagocytic blood cells and haemoglobin ducts). The vasa deferentia run up to 18th segment where which is dissolved in blood plasma. they join the prostatic duct. Respiratory system The common prostate and spermatic duct open to the exterior by a pair of male genital pores on the ventro-lateral - No specialized system. side of the 18th segment. - Gas exchange occurs through moist body surface into the Accessory glands: 2 pairs. Found in the 17th & 19th blood stream. segments (one pair in each segment). Excretory system Excretory organs are segmentally arranged tubules called nephridia. They are 3 types: a. Septal nephridia: Found on both sides of intersegmental septa (segment 15 to last) that open into intestine. b. Integumentary nephridia: Attached to lining of body wall (segment 3 to last). They open on body surface. Female reproductive organs: c. Pharyngeal nephridia: Present in the 4th, 5th & 6th Spermathecae: 4 pairs. Located in 6th-9th segments (one segments in the form of paired tufts. pair in each segment). They receive and store spermatozoa Funnel-shaped part of nephridium collects excess fluid from during copulation. coelom. The funnel connects with a tubular part of Paired ovaries: Attached at the inter-segmental septum of nephridium which delivers the wastes into digestive tube. the 12th and 13th segments. Ovarian funnels: Present beneath the ovaries which Nervous system continue into oviduct, join together and open on ventral side - Includes segmentally arranged ganglia on the ventral as single median female genital pore on 14th segment. paired and fused nerve cord. - During mating, two worms exchange sperms each other. - The nerve cord in the anterior region (3rd & 4th segments) They mate juxtaposing opposite gonadal openings divides and encircles the pharynx and joins the cerebral exchanging spermatophores (packets of sperms). ganglia dorsally to form a nerve ring. - Mature sperm, ova and nutritive fluid are deposited in - The nerve ring with cerebral ganglia represents the brain. cocoons produced by gland cells of clitellum. Cocoon with - Sensory system: Includes fertilized ova slips off and deposit in the soil. After 3 weeks, Light and touch sensitive receptor cells. No eyes. cocoon produces 2 to 20 baby worms (no larva). Chemoreceptors (taste receptors): React to chemical ECONOMIC IMPORTANCE stimuli. - Earthworms are known as ‘friends of farmers’ because they Reproductive system make burrows in the soil and make it porous which helps in Earthworm is hermaphrodite. respiration and penetration of the plant roots. This process of Male reproductive organs: increasing fertility of soil is called vermicomposting. - They are used as bait in game fishing. 7  MORPHOLOGY & ANATOMY OF FROG Systematic position - Digestion: Gastric juice and HCl secreted from gastric wall Phylum : Chordata digest the food. Partially digested food (chyme) is passed from stomach to the duodenum. Class : Amphibia Duodenum receives bile and pancreatic juices through a Genus : Rana common bile duct. Species : tigrina Bile emulsifies fat. Pancreatic juice digests carbohydrates Rana tigrina is the most common species in India. and proteins. Digestion completes in the intestine. They are poikilotherms (cold blooded). - Finger-like villi and microvilli in intestine absorb digested They can change colour to hide them from their enemies food. The undigested solid waste moves into the rectum and (camouflage). This protective coloration is called mimicry. passes out through cloaca. During summer and winter, they undergo aestivation (summer sleep) and hibernation (winter sleep) Respiratory system respectively to protect them from extreme heat and cold. - Skin acts as aquatic respiratory organ (cutaneous respiration). Dissolved oxygen in the water is exchanged MORPHOLOGY OF FROG through the skin by diffusion. During aestivation and Body is divisible into head & trunk. Neck and tail absent. hibernation respiration takes place through skin. Skin is moist, smooth and slippery due to the mucus. - On land, the buccal cavity, skin and lungs (pulmonary Colour of dorsal side is olive green with dark irregular spots respiration) act as the respiratory organs. and ventral side is pale yellow. - The lungs are a pair of elongated, pink coloured sac-like The frog never drinks water but absorb it through the skin. structures present in the thorax. Air enters through the A mouth, paired nostrils and bulged eyes (covered by nostrils into the buccal cavity and then to lungs. nictitating membrane) are present. On either side of eyes have a membranous tympanum (ear). Circulatory system The forelimbs (4 digits) and hind limbs (5 digits) help in - Closed type. Includes Blood vascular system (heart, swimming, walking, leaping and burrowing. The hind blood vessels & blood) and lymphatic system (lymph, limbs are larger and muscular than fore limbs. lymph channels & lymph nodes). Feet have webbed digits that help in swimming. - Heart is 3-chambered, (two atria and one ventricle) and is Frogs exhibit sexual dimorphism. Male frogs have sound covered by a membrane called pericardium. producing vocal sac and also a copulatory (nuptial) pad on - A triangular structure called sinus venosus joins the right the first digit of fore limbs which are absent in female frogs. atrium. It receives blood through major veins (vena cava). - The ventricle opens into a saclike conus arteriosus on the ANATOMY OF FROG ventral side of the heart. - The blood pumped from the muscular heart is carried to all parts of the body by the arteries (arterial system). - The veins collect blood from different parts of body to the heart and form the venous system. - Hepatic portal system (venous connection between liver and intestine) and renal portal system (between kidney and lower parts of the body) are present in frogs. - Blood contains plasma and cells (RBC, WBC & platelets). RBCs are nucleated and contain haemoglobin. - Blood transports nutrients, gases and water to tissues. Excretory system - Includes kidneys (2), ureters (2), cloaca & urinary bladder. - Kidneys are dark red and bean-shaped. Found posteriorly in Digestive system the body cavity on both sides of vertebral column. Each - Consists of alimentary canal and digestive glands. kidney is formed of uriniferous tubules (nephrons). - The alimentary canal is short because frogs are carnivores and - 2 ureters emerge from the kidneys. In male frogs, the ureters hence the length of intestine is reduced. act as urinogenital duct which opens into cloaca. - Mouth → buccal cavity → pharynx → oesophagus → In females, ureters & oviduct open separately in cloaca. stomach → intestine → rectum → cloaca. - The thin-walled urinary bladder is present ventral to the - Liver secretes bile that is stored in gall bladder. Pancreas rectum which also opens in the cloaca. produces pancreatic juice containing digestive enzymes. - The frog is a ureotelic animal (excretes urea). Nitrogenous - Food is captured by the bilobed tongue. wastes are carried by blood into the kidney where it is separated and excreted. 8  Control and co-ordination - Male reproductive organs consist of a pair of yellowish ovoid testes, which are found adhered to the upper part of kidneys Endocrine system by a double fold of peritoneum (mesorchium). - The endocrine glands secrete hormones. - Vasa efferentia (10-12 in number) arise from testes. They - Endocrine glands: pituitary, thyroid, parathyroid, thymus, enter the kidneys on their side and open into Bidder’s canal. pineal body, pancreatic islets, adrenals & gonads. It communicates with urinogenital duct that comes out of the Nervous system kidneys and opens into cloaca. It includes - The cloaca is a small, median chamber that is used to pass Central nervous system (brain & spinal cord), faecal matter, urine and sperms to the exterior. Peripheral nervous system (cranial & spinal nerves) Autonomic nervous system (sympathetic & parasympathetic). - There are 10 pairs of cranial nerves arising from brain. - Brain is enclosed in a bony brain box (cranium). - The brain is divided into Fore-brain: Includes olfactory lobes, paired cerebral hemispheres and unpaired diencephalon. Mid-brain: Includes a pair of optic lobes. Hind-brain: Includes cerebellum & medulla oblongata. - Medulla oblongata passes out through the foramen magnum and continues into spinal cord, which is enclosed in the vertebral column. - Sense organs include organs of Sensory papillae: For touch Taste buds: For taste - The female reproductive organs include a pair of ovaries. Nasal epithelium: For smell The ovaries are situated near kidneys and there is no Simple eyes: For vision. Paired and situated in orbit functional connection with kidneys. Tympanum with internal ears: For hearing and - A pair of oviduct arising from the ovaries opens into the balancing (equilibrium). cloaca separately. - A mature female can lay 2500 to 3000 ova at a time. Reproductive system - Fertilisation is external and takes place in water. - Development involves a larval stage called tadpole. - Tadpole undergoes metamorphosis to form the adult. ECONOMIC IMPORTANCE - Frogs are beneficial for mankind because they eat insects and protect the crop. - Maintain ecological balance by serving as an important link of food chain and food web in the ecosystem. - In some countries the muscular legs of frog are used as food by man. 9