Frog - Digestive And Reproductive System

Amphibian development involves a marked change of body form, and NCERT describes the frog's indirect life cycle. After external fertilisation the eggs hatch into a free-swimming aquatic larva called the tadpole, which possesses gills for aquatic respiration and a tail for swimming; it later undergoes metamorphosis to become the adult frog that breathes through lungs and skin. A cocoon is the protective egg case made by structures like the earthworm's clitellum and is not a respiring larval stage of the frog. A nymph is the immature stage of insects with incomplete metamorphosis, such as the cockroach, resembling a small adult and never possessing fish-like gills of an amphibian larva. A pupa is the resting transformation stage of insects with complete metamorphosis and does not respire through gills in water. As stated in NCERT Class 11, Chapter 7 (Structural Organisation in Animals), the frog's tadpole undergoes metamorphosis into the adult. A developmental order check confirms that gilled aquatic larval respiration belongs only to the tadpole stage.