Systematic Position of Frog
Phylum: Chordata
Group: Vertebrata
Subphylum: Gnathostomata
Superclass: Tetrapoda
Class: Amphibia
Order: Anura
Genus: Rana
Species: tigrina
New name – Hoplobatrachus tigerinum
General Characteristics of Frog
A. Habitat· It is cosmopolitan in distribution.
· It exhibits amphibious mode of life i.e. aquatic as well as terrestrial found near ditches, pools, ponds or other stagnant water bodies.
· This amphibious mode of adaptation is called stenohygrous.
B. Habit
i. Locomotion:
B. Habit
i. Locomotion:
· It occurs in the following ways.
(a) Jumping and leaping
(b) Swimming
(a) Jumping and leaping
(b) Swimming
(c) Rarely walking
ii. Feeding:
· Exclusively carnivorous.
· Tadpoles are herbivorous.
· Also, exhibit cannibalism during starvation.iii. Croaking or mating or sex-call:
· The sound of male frogs is louder than in females.
· It is because male frogs have two vocal sacs which act as resonators.
· It is a mating call to attract females.
iv. Hibernation:
· It is also called winter sleep.
· During this time, only cutaneous respiration occurs.
v. Aestivation:
· It is also called summer sleep.
· The frog rests and stores its energy.
vi. Protective colouration or camouflage:
· It is the phenomenon to match the body colour according to the background to escape from enemies and catch prey.
· It is also called colour mimicry.
A. Division of the body:
External Features of Frog
· Body of the frog is bilaterally symmetrical, spindle-shaped, streamlined and somewhat dorsoventrally flattened.A. Division of the body:
· The body can be divided into head and trunk.
· No neck.
· No tail but tail is present in the tadpole stage.
B. Head:
· Head is triangular and somewhat flattened.
 |
| External features of frog |
C. Mouth:
· It lacks lips and cheeks.
· It helps in the ingestion of prey.
D. External nares:
· Two valvular external nares one on each side of the snout open into the buccopharyngeal cavity.
E. Eyes:
· On the dorsolateral side of the head, two prominent bulging eyes are located.
· The eyes are covered with thick pigmented immovable upper eyelid and rudimentary and movable lower eyelid.
· A third eyelid called the Nictitating membrane is also present. It is an extension of the lower eyelid which. It is semi-transparent, freely movable. They are used for binocular vision and compensate for the absence of the neck.
· A third eyelid called the Nictitating membrane is also present. It is an extension of the lower eyelid which. It is semi-transparent, freely movable. They are used for binocular vision and compensate for the absence of the neck.
F. Brow spot:
· It is located just in front of two eyes that represents the 3rd eye of their ancestors.
· Two circular tympanic membranes or eardrums are located behind and below the eye.
· Two circular tympanic membranes or eardrums are located behind and below the eye.
· NO external ear.
· Ventral surface of the head in males contains two bluish patches of vocal sacs which act as resonators during the production of croaking sound.
· Between anterior borders of eyes along the mid-dorsal line is present. It extends from the tip of the snout to the cloacal aperture.
· Between anterior borders of eyes along the mid-dorsal line is present. It extends from the tip of the snout to the cloacal aperture.
G. Trunk:
· The trunk is short, broad and somewhat flattened with dorsolateral dermal plicae and a characteristic dorsal hump.
· At the posterior end of the trunk, a cloacal aperture is present. It is a common opening for releasing out faeces, urine and gametes.
· At the posterior end of the trunk, a cloacal aperture is present. It is a common opening for releasing out faeces, urine and gametes.
· Attached to the lateral sides of the trunk, there are a pair of forelimbs and a pair of hind limbs.
H. Forelimbs:
H. Forelimbs:
· They are shorter, weaker, smaller and without webs.
· Each forelimb consists of three parts:
· Upper arm (Brachium)
· Forearm (Antebrachium)
· Wrist
a. Hand/Manus:
· Upper arm (Brachium)
· Forearm (Antebrachium)
· Wrist
a. Hand/Manus:
· It consists of a palm and 4 digits.
· NO THUMB.
· Index finger has a rough pad-like swelling called Nuptial or Amplexary or Copulatory pad. It is present only in males during the breeding season.
· Digital formula for forelimbs: 0, 2, 2, 3, 3
· Digital formula for forelimbs: 0, 2, 2, 3, 3
I. Hind limbs:
· The two hindlimbs are longer, larger, stronger and muscular.
· Each hindlimb consists of three parts:
· Thigh (Femur)
· Shank (Crus)
· Ankle
a. Foot or pes:
· Thigh (Femur)
· Shank (Crus)
· Ankle
a. Foot or pes:
· It consists of 5 webbed digits.
· It also contains subarticular pads on the ventral surface of toes without claws.
· Digital formula for hind limbs: 2, 2, 3, 4, 3
· Digital formula for hind limbs: 2, 2, 3, 4, 3
· Sexual dimorphism is well-marked with the male having a smaller and sturdy body, vocal sacs, copulatory pads and greater development of musculature.
SEXUAL DIMORPHISM IN FROG
· Sexual dimorphism: There are some differences in external characters by which male and female frogs can be distinguished. These are as follows.| S.N | Male Frogs | Female Frogs |
|---|---|---|
| 1. | Smaller in size. | Larger in size. |
| 2. | Darker in colour. | Lighter in colour. |
| 3. | Due to the presence of vocal sacs, they croak loudly. | Vocal sacs are absent. |
| 4. | Males are slimmer. | Females are stouter especially when they contain eggs. |
| 5. | Forelimbs are relatively thick and muscular. The inner digit of the forelimb has a glandular swelling- nuptial pad at the ventral side. | Nuptial pads are lacking in females. |
Difference between Articular and Nuptial pads in Frog.
| S.N | Articular pads | Nuptial pads |
|---|---|---|
| 1. | These are present in the forelimbs of the male and female frogs. | These are present only in the males on the ventral side of the first finger of each forelimb. These pads are used to grip a female during amplexus. |
Skin of Frog
· The skin of the frog is smooth, moist, slippery and naked (i.e. devoid of scales or other exoskeletons).· It is olive-green dorsally and creamy white ventrally.
· The special functions of the skin are cutaneous respiration and protective colouration, digestion too due to the secretion of diastase enzyme. But, it does not play role in thermoregulation unlike that of the mammalian skin.
· The special functions of the skin are cutaneous respiration and protective colouration, digestion too due to the secretion of diastase enzyme. But, it does not play role in thermoregulation unlike that of the mammalian skin.
A. Histological Structure
· The skin consists of the epidermis and dermis.
a. Epidermis:
· It is the outermost, non-vascularised and stratified squamous epithelium.
· It consists of two layers: stratum corneum and stratum spongiosum.
i) Stratum corneum:
· It consists of two layers: stratum corneum and stratum spongiosum.
i) Stratum corneum:
· It is formed by stratified squamous epithelium having 4-5 layers of dead cells which is protective in function and cast off once a month (moulting).
b) Stratum germinativum (Malpighian layer):
b) Stratum germinativum (Malpighian layer):
· It is formed by a single layer of columnar cells and rests on a basement membrane.
b. Dermis:
· It consists of connective tissue, muscle fibres, nerve fibres, blood vessels, cutaneous glands and chromatophores.
· The dermis is divisible into stratum spongiosum and stratum compactum.
i) Stratum spongiosum:
· The dermis is divisible into stratum spongiosum and stratum compactum.
i) Stratum spongiosum:
· It contains cutaneous glands and chromatophores.
· The stratum spongiosum contains two types of cutaneous glands which are Mucous glands and Poison glands.
· These glands are formed by the invagination of stratum germinativum.
· Frogs are capable of changing the colour of the skin due to the presence of chromatophores.
· These glands are formed by the invagination of stratum germinativum.
· Frogs are capable of changing the colour of the skin due to the presence of chromatophores.
· This phenomenon of colour change is called Metachrosis.
· The chromatophores are present in the stratum spongiosum just beneath the stratum germinativum. They are of 3 types:
i. Lipophores: They contain Red and yellow pigments.
ii. Melanophores: They contain Black and brown pigments.
iii. Guanophores: They contain White pigment.
· The chromatophores are present in the stratum spongiosum just beneath the stratum germinativum. They are of 3 types:
i. Lipophores: They contain Red and yellow pigments.
ii. Melanophores: They contain Black and brown pigments.
iii. Guanophores: They contain White pigment.
ii) Stratum compactum
· It has collagen fibres.
Note:
· The skin of a frog doesn't play the role of maintaining thermoregulation but is responsible for osmoregulation.
· It doesn't synthesize the vitamin-D and does not yield the leather due to thin dermis.
1. Jumping on land
Note:
· The skin of a frog doesn't play the role of maintaining thermoregulation but is responsible for osmoregulation.
· It doesn't synthesize the vitamin-D and does not yield the leather due to thin dermis.
Locomotion in Frog
· It takes place in 3 ways.1. Jumping on land
2. Swimming in water
3. Walking on land
· Hind limbs are folded as z–shaped that act as spring whereas shorter forelimb helps to change the direction during jumping.
· Webbed feet of hind limbs help in swimming that acts as a paddle in the water.
· Inactive hiding period to protect from freezing temperature.
· Feeding and locomotion are totally arrested.
· Note – In hibernation, frog respires through the skin (cutaneous respiration).
· At that time, it becomes uricotelic.
· Hind limbs are folded as z–shaped that act as spring whereas shorter forelimb helps to change the direction during jumping.
· Webbed feet of hind limbs help in swimming that acts as a paddle in the water.
Dormant period (Inactive periods)
A. Hibernation (Winter sleep)· Inactive hiding period to protect from freezing temperature.
· Feeding and locomotion are totally arrested.
· Note – In hibernation, frog respires through the skin (cutaneous respiration).
· At that time, it becomes uricotelic.
B. Aestivation (Summer sleep)
· It is an inactive period to protect from the drought.
· Duration: 1 to 15 days
· It is an inactive period to protect from the drought.
· Duration: 1 to 15 days
· Frog becomes sluggish but can feed the food.
· Frog respires through the skin (cutaneous respiration).
Camouflage or Colour Mimicry or Protective Colouration
· It is a phenomenon of change of body colour according to the background of animal to escape from enemies.
· The ability to change body colour is called metachrosis.
· It is due to the presence of chromatophores.
· Frog respires through the skin (cutaneous respiration).
Camouflage or Colour Mimicry or Protective Colouration
· It is a phenomenon of change of body colour according to the background of animal to escape from enemies.
· The ability to change body colour is called metachrosis.
· It is due to the presence of chromatophores.
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