Frogs – Morphology and Anatomy

General Characteristics

• Frogs are carnivorous, tailless amphibians, commonly found in India.
• Species in India are known as Rana tigrina.
• Belong to the class Amphibia, phylum Chordata.
• They are cold-blooded animals (poikilotherms):
  • Body temperature changes with the environment.
  • Undergo aestivation in summer and hibernation in winter.
• Capable of camouflage by changing skin color according to surroundings.

Morphology

• Adult frogs have a stout body divided into head and trunk.
• Features include:
  • Nostrils, protruding eyes, tympanum (ear).
  • Moist, slippery/warty skin.
  • Webbed limbs.
• Skin:
  • Highly permeable and acts as a respiratory organ.
  • Produces mucus and toxins to deter predators.
• Locomotion via forelimbs and hind limbs.
• Unisexual with sexual dimorphism:
  • Males: Vocal sacs and copulatory pads on forelimbs.
  • Females: Lack these features.

Anatomy

Digestive System

• Composed of alimentary canal and accessory organs.
• Frogs are carnivorous with a short intestine.
• Alimentary canal sequence: Mouth → Pharynx → Oesophagus → Stomach → Small intestines → Large intestines → Rectum → Cloaca.

Respiratory System

• Two modes: Cutaneous and pulmonary respiration.
• In water: Cutaneous respiration via skin.
• On land: Combination of skin and lungs.
• During aestivation/hibernation: Only skin is used.

Circulatory System

• Muscular heart with three chambers: Two atria, one ventricle.
• Blood and lymph transport substances through vessels.

Excretory System

• Ureotelic animals excreting urea.
• Composed of kidneys, ureters, cloaca, and urinary bladder.
• Nephrons filter blood and excrete waste.

Coordination System

• Composed of nervous and endocrine systems.
• Endocrine glands: Pituitary, thyroid, parathyroid, thymus, pineal body, pancreatic islets, adrenals, and gonads.
• Nervous System:
  • Divided into CNS and PNS.
  • Brain has forebrain, midbrain, and hindbrain.

Reproductive System

• Male frogs have testes for sperm production, ejected via cloaca.
• Female frogs have ovaries producing ova, passed to oviduct and then cloaca.
• External fertilization of 2500 to 3000 eggs.