Give an example of metamorphosis in animals. What are the changes observed during metamorphosis of this animal?

The frog provides a classic example of metamorphosis, undergoing dramatic transformation from aquatic tadpole to terrestrial or semi-aquatic adult. Frog metamorphosis begins when eggs hatch into tadpoles—small, fish-like larvae with streamlined bodies, long muscular tails for swimming, and gills for extracting oxygen from water. During this larval stage, tadpoles are primarily herbivorous, feeding on algae and plant matter using specialized scraping mouthparts, and possess a simple, single-loop circulatory system adapted for aquatic life.

As metamorphosis progresses over several weeks to months (duration varies by species and environmental conditions), tadpoles undergo profound structural and physiological changes. Hind limbs emerge first, followed by front limbs, while the tail gradually shortens through programmed cell death and tissue resorption, with nutrients recycled to fuel other developmental changes. The respiratory system transforms as gills degenerate and functional lungs develop, accompanied by circulatory system modifications to support air-breathing. The digestive tract shortens and restructures to accommodate a carnivorous diet of insects and invertebrates. Eyes migrate to more prominent positions, the mouth widens, and a true tongue develops for catching prey. Skin changes occur as the tadpole develops mucous glands and pigmentation suitable for terrestrial life. These changes are orchestrated by thyroid hormones, particularly thyroxine, which trigger the genetic programs controlling metamorphic development. The transformation from water-bound, plant-eating tadpole to air-breathing, insect-eating frog represents one of nature's most remarkable developmental processes, allowing different life stages to exploit separate ecological niches and resources.