Fig. 3. Cross-section of a lung sac in (A) normal X. laevis tadpole, (B) giant X. laevis tadpole with inflated lungs and (C) giant X. laevis tadpole with solidified lungs. Sections are stained with Hematoxylin and Eosin. Inflated lungs in giants are functional, but more septa are present than in normal tadpoles' lungs. Solidified lungs in giants show numerous septa and little air space. Dark melanocytes are present in all lungs. (D) Cross-section through a septum of a solidified lung, stained with Masson's Trichrome. Abundant collagen (blue) is present in the walls and septa of solidified lungs. Smooth muscle tissue (red) is lining a blood vessel. Scale bars, 200 µm (A–C); 50 µm (D).