नेपाली व्याकरण

Rana tigrina, also known as the Indian Bullfrog, is a large frog found in South and Southeast Asia, including Nepal, India, and Bangladesh. It usually lives near ponds, fields, and wetlands. This frog has a greenish body with black spots and a pale yellow belly. During the monsoon season, male frogs turn bright yellow to attract females for breeding. It eats insects, small animals, and even other frogs. Rana tigrina is important for the environment because it helps control pests and maintains the balance of nature.

Classification

Common Name Rana tigrina

Local Name Barsati mendak

Other Name Indian bullfrog/Tiger frog

Zoological Name Hoplobatrachus tigerinus

Kingdom Animalia

Phylum-Chordata

Class-Amphibia

Order-Anura

Family Dicroglossidae

Genus-Hoplobatrachus

.Habitat:

Prefers freshwater wetlands and aquatic areas.

Avoids coastal and forest regions.

Lives in holes and bushes near permanent water sources.

Spends most of its time hiding and feeding in surrounding vegetation.

Habits:

Mostly solitary and active at night (nocturnal).

Feeds on insects, invertebrates, mice, earthworms, young frogs, juvenile snakes, and small birds.

Breeding:

Breeds during the monsoon, soon after the first rain.

Males gather in rainwater pools and turn bright yellow, earning the local name "Basanti Dadoo."

Females remain dull in color.

Male frogs make a loud "Cronk, cronk" sound to attract females.

During mating, males compete by jumping over each other and fighting to hold onto the female.

External Features of Rana tigrina (Frog):

1. Body Structure:

Divided into head and trunk; no neck or tail.

Skin is moist, smooth, and slippery due to mucus secretion.

The skin can absorb water.

2. Color:

Dorsal side: Dark green with irregular spots.

Ventral side: Pale yellow.

3. Head Features:

Triangular shape with a blunt snout.

Eyes have a nictitating membrane for protection underwater.

Tympanum (ear) on the sides of the eyes receives sound signals.

4. Limbs:

Two forelimbs and two hind limbs assist in walking, swimming, leaping, and burrowing.

5. Sexual Dimorphism:

Males have vocal sacs and a copulatory pad (absent in females).

Shape and Size:

1. Streamlined Body:

Designed for both aquatic and aerial life, aiding in swimming.

2. Body Ends:

Anterior and posterior ends are pointed.

Triangular flattened head connected directly to the trunk without a neck.

3. Tail:

Absent in adult frogs.

External Features of Frog:

1. Size:

Size varies across species and age, ranging from a few centimeters to many centimeters.

2. Color:

Dorsal side: Green with black spots and streaks.

Ventral side: Paler, blending with the environment for camouflage.

3. Skin:

Smooth, thin, moist, and slimy.

Loose-fitting with longitudinal folds on the back called dermal plicae.

4. Body Division:

Divided into head and trunk.

No neck or tail (present only in tadpoles).

Head and trunk are broadly connected.

5. Head Features:

Shape: Triangular, flattened with a blunt apex (snout).

Mouth: Large and transverse, located at the tip of the snout.

Nostrils: Two lateral external nares at the snout's tip, connecting to the buccal cavity for respiration.

Eyes: Two large, prominent, bulging eyes on the dorsolateral side of the head.

External Features of Frog (Head):

I. Eyes:

Positioned to provide a wide field of vision, compensating for the absence of a neck.

Protection:

1. Upper eyelid: Thick, fleshy, opaque, and immovable.

2. Lower eyelid: Thin, transparent, movable, capable of covering the eye.

3. Nictitating membrane: Transparent third eyelid (part of the lower eyelid), covers the eyeball in water and keeps it moist in air.

Frog can see through the nictitating membrane.

II. Vestigial Pineal Eye:

Light-colored patch (brown spot) on the middle of the head, representing a vestigial pineal eye.

III. Ears (Tympanic Membrane):

No external ears.

Nearly circular, tough, transparent tympanic membrane located obliquely behind and below each eye, functioning as the ear drum.

IV. Vocal Sacs (Male Frogs):

Two bluish, wrinkled patches of skin under the head, used to produce croaking sounds to attract females for copulation.

External Features of Frog (Trunk):

I. Trunk Structure:

Broadly joined to the head, short, somewhat flattened, and ovoid.

Sacral Hump: A prominent feature on the dorsal side due to the linking of the hip girdle to the vertebral column.

II. Cloacal Opening:

Located at the posterior end of the trunk between the hindlimbs.

Functions as the common exit for faecal matter, urine, and reproductive materials (sperms and ova).

III. Limbs:

Forelimbs:

1. Shorter than hindlimbs, used for holding and supporting the body during jumping.

2. Composed of:

Upper Arm (Brachium)

Forearm (Antebrachium)

Wrist and Hand (Manus) with four fingers and a vestigial thumb (pollex).

3. Males have a thickened base of the inner finger (nuptial pad) during the breeding season for clasping females during amplexus.

Hindlimbs:

1. Larger and used for jumping and swimming.

2. Composed of:

Thigh

Shank (Lower Leg)

Ankle (Tarsus)

Foot with five slender toes connected by broad, thin webs of skin for swimming.

3. Foot has a narrow sole.

IV. Adaptations for Movement:

Forelimbs support the body during jumping.

Hindlimbs, with their webbed toes, assist in both jumping and swimming.

Coelom and Viscera (Internal Organs):

I. Coelom (Body Cavity):

The coelom is large and spacious, providing space for internal organs.

It lies ventral (toward the belly) to the vertebral column (backbone).

II. Viscera (Internal Organs):

The coelom houses various internal organs, such as the heart, lungs, liver, and digestive system.

These organs are essential for the frog's survival, providing functions like digestion, circulation, and respiration.

III. Peritoneum:

The body cavity and visceral organs are covered by a thin, moist membrane called the peritoneum.

This membrane is continuous throughout the body and is reflected over the various organs, providing protection and lubrication.

Peritoneum and its Layers:

I. Visceral Layer:

The portion of the peritoneum that surrounds the alimentary canal (digestive system) and its appendages (such as the liver and intestines) is called the visceral layer.

This layer provides a protective covering and supports the organs involved in digestion.

II. Parietal Layer:

The part of the peritoneum that is applied to the body wall is called the parietal layer.

It helps in covering and supporting the body cavity.

III. Subvertebral Lymph Space:

On the dorsal (back) side of the body, the parietal layer is separated from the body wall, creating a large lymph space called the subvertebral lymph space.

This space contains the kidneys, which are covered by the peritoneum on the ventral (front) side.

The kidneys are important for excretion and are protected within this space by the peritoneum.

Alimentary Canal and Gonads:

I. Mesentery:

The alimentary canal (digestive tract) and gonads (reproductive organs) are suspended from the dorsal body wall by a thin sheet of membrane called the mesentery.

The mesentery provides support and helps in maintaining the position of these organs.

II. Coelomic Fluid:

The coelom, or body cavity, is filled with a transparent coelomic fluid that resembles lymph.

This fluid helps in cushioning and protecting internal organs.

III. Heart and Pericardium:

Near the anterior end of the body cavity is the heart, which is enclosed in a transparent sac called the pericardium.

The pericardium provides protection and support to the heart.

Skin:

I. Structure:

The skin is smooth, moist, and slippery, lacking external protective scales or hairs.

It is loosely attached to the underlying musculature by thin connective tissue bands, making the animal easy to skin.

The skin is thicker on the dorsal (top) side of the body compared to the ventral (bottom) side.

II. Dorsolateral Dermal Plicae:

On the dorsal side of the body, the skin is thrown into folds, forming dorsolateral dermal plicae (ridges).

These folds extend from behind the eyes and help in the movement and flexibility of the frog's body.

III. Coloration:

The skin on the back and limbs is dark green with dark streaks and patches, providing camouflage in its natural environment.

The ventral (underneath) side of the body is pale yellow, helping the frog blend in with its surroundings when viewed from below.

Structure of the Skin:

The skin of the frog, like other vertebrates, consists of two main layers: epidermis and dermis.

Epidermis:

I. Outer Layer:

The epidermis is the outermost layer of the skin. It is non-vascular (does not contain blood vessels) and stratified (composed of multiple layers of cells).

This layer is shed and renewed at regular intervals through a process called moulting.

II. Stratum Corneum:

The outermost layer of the epidermis is called the stratum corneum.

It consists of flattened, squamous epithelial cells that are keratinized (hardened). This layer helps protect the body from external damage and prevents water loss.

III. Stratum Germinativum (Stratum Malpighii):

The innermost layer of the epidermis is the stratum germinativum or stratum Malpighii.

This layer is composed of active columnar epithelial cells that continuously produce new cells.

As these new cells move towards the surface, they gradually become flattened and lose their columnar shape, eventually transforming into keratin (a tough, protective substance).

The process of cell transformation helps to form the tough outer layer that provides protection to the frog's skin.

Skin Structure of the Frog (continued)

Epidermis (continued):

IV. Moulting:

As the old cells of the stratum corneum are worn out due to friction, they are replaced by new cells formed by the stratum germinativum (also called stratum Malpighii).

The stratum corneum is shed periodically, and the frog often eats the shed skin. This process is known as moulting, which is regulated by the secretions of the thyroid and pituitary glands.

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Dermis:

The dermis is a flexible, somewhat elastic layer beneath the epidermis. It consists of two layers:

I. Stratum Spongiosum:

This is the outer, loose layer of the dermis, consisting of a loose network of fibrous connective tissue.

It is rich in lymph spaces and blood vessels.

The stratum spongiosum contains pigment cells that give color to the skin. These cells have irregular shapes and branched processes, and they contain black and yellow pigments.

In the deeper part of this layer, various glands are embedded.

II. Stratum Compactum:

This is the inner, dense layer of the dermis composed of fibrous connective tissue. The fibers in this layer run in a wavy pattern parallel to the skin surface.

This layer also contains smooth muscle fibers, elastic fibers, nerves, and blood vessels.

Vertical strands in this layer extend through the stratum spongiosum and reach the epidermis.

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Subcutaneous Connective Tissue:

Beneath the stratum compactum, there is a loose layer of subcutaneous connective tissue.

This is followed by another very thin layer close to the muscles.

These two layers are separated by large lymph spaces, except in the septa, where they become continuous.

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Glands:

There are two types of glands found in the frog's skin:

1. Mucous Glands: These glands secrete mucus that keeps the skin moist and helps with respiration through the skin.

2. Poison Glands: These glands produce toxic substances that can serve as a defense mechanism against predators.

Both types of glands are derivatives of the epidermis, but they are located in the stratum spongiosum of the dermis.

Mucous Glands:

Shape and Structure: The mucous glands are flask-shaped and found in abundance across the body surface, especially on the dorsal side and hindlegs, particularly in the dermal plicae.

Epithelium: The gland body is lined by a single layer of epithelial cells, except near the neck opening, where there are two layers.

Function: These glands secrete colorless, watery mucus that keeps the skin moist, glistening, and sticky, helping in hydration and respiration through the skin. The mucus is expelled through the gland’s neck, and the muscular coat of smooth muscle cells helps with the expulsion of the mucus.

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Poison Glands:

Structure: Poison glands are also lined with epithelial cells, which are cylindrical and filled with granules. They have a single epithelial layer and communicate with the outside through narrow ducts.

Secretion: The secretion of the poison glands is a whitish fluid with a burning taste, which serves as a defensive mechanism by protecting the frog from predators.

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Functions of the Skin:

The skin of the frog serves several important functions:

1. Protection: It gives the body a definite shape and texture and acts as a protective covering against physical harm and environmental threats.

2. Defense: It helps protect the body against foreign bodies and fungal spores.

3. Moisture and Hydration: The mucous glands keep the skin moist, glistening, and sticky. The mucus also helps in preventing harmful materials and waterborne contaminants from invading the frog’s body.

Functions of the Skin (Continued):

4. Respiratory Function: The skin serves as a primary respiratory organ. Its moist surface allows for the exchange of respiratory gases, oxygen (O₂) and carbon dioxide (CO₂), between the frog's body and the environment.

5. Excretory Role: Since frogs do not have sweat glands, the skin acts as an excretory organ. The shedding of the stratum corneum (outer skin layer) helps eliminate excretory waste and substances no longer needed by the body.

6. Sensory Function: Due to the presence of nerve endings, the skin functions as an important sensory organ, allowing the frog to detect changes in its environment.

7. Water Absorption: Frogs do not drink water through the mouth; instead, they absorb water through their skin. The skin, with its loosely attached structure, allows water to collect in the large subcutaneous lymph spaces, helping maintain hydration.

8. Hatching Function: In frog larvae, the skin produces hatching enzymes that dissolve the egg membrane, facilitating hatching.

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Digestive System of a Frog:

The digestive system of a frog is responsible for processing food, breaking it down into nutrients, and absorbing them for use by the body. It includes the following parts:

1. Mouth: The entry point for food, where initial ingestion begins.

2. Pharynx: The passage that connects the mouth to the esophagus.

3. Esophagus: A tube that transports food from the mouth to the stomach.

4. Stomach: The organ where food is broken down by digestive enzymes and acids.

5. Small Intestine: The site for the absorption of nutrients from the digested food.

6. Large Intestine: Absorbs water and forms feces.

7. Cloaca: A common chamber where the digestive, excretory, and reproductive tracts meet.

8. Cloacal Aperture: The external opening through which waste and reproductive bodies are expelled.

This system works together to ensure that the frog properly processes its food and removes waste efficiently.

Here’s the digestive system of a frog in simple points:

1. Mouth: Food is taken in through the mouth. Frogs catch food with their sticky tongue.

2. Teeth: Frogs have weak teeth, called maxillary teeth, which help grind food a little.

3. Saliva: The salivary glands produce saliva to break down starch into sugar and add moisture to the food.

4. Pharynx: After the food is mixed with saliva, it moves into the pharynx.

5. Oesophagus: The food then passes into the oesophagus (food pipe) and moves to the stomach.

6. Stomach: In the stomach, food is mixed with digestive fluids and broken down by enzymes.

7. Small Intestine: The partially digested food moves into the small intestine, where most digestion occurs.

Duodenum and Ileum are parts of the small intestine.

The pancreas and liver secrete digestive juices (pancreatic juice and bile) to help digestion.

8. Absorption: Nutrients from the digested food are absorbed in the small intestine.

9. Large Intestine: Any unabsorbed food and water move into the large intestine, where water is reabsorbed.

10. Waste: Liquid waste is stored in the urinary bladder, while solid waste moves to the cloaca.

11. Cloaca: Both liquid and solid wastes are expelled through the cloaca.

This process helps the frog digest and absorb nutrients, and get rid of waste.

Here is a simplified breakdown of how food is ingested and digested in a frog:

1. Ingestion:

The frog uses its sticky tongue to catch food (like insects).

The teeth in the mouth help hold the food, and the frog swallows it whole.

2. Esophagus:

After swallowing, food moves through the short esophagus to the stomach.

3. Stomach:

The stomach is where food is held temporarily.

Gastric glands release gastric juices containing hydrochloric acid (HCl) and enzymes that start breaking down food.

4. Pylorus:

After digestion in the stomach, food enters the pylorus, where a muscular valve controls its passage to the small intestine.

5. Small Intestine:

The food moves to the small intestine where bile (produced by the liver) and pancreatic juices (from the pancreas) aid in digestion.

Intestinal enzymes break down the food further so nutrients can be absorbed.

6. Absorption:

Nutrients from the digested food are absorbed in the small intestine.

7. Waste:

The leftover undigested food moves to the large intestine for water absorption.

The waste is expelled through the cloaca.

Thus, the frog's digestive system involves multiple organs and enzymes to break down food and absorb nutrients.