Figure 2

(A–F) Histological sections stained with hematoxylin and eosin showing the various structural components of the lungs of the semifossorial African giant pouched mole rat (Cricetomys gambianus) (A) and that of the underground-dwelling (subterranean) Nigerian mole rat (Cryptomys foxi) (B). BV, blood vessels larger than blood capillaries; Br, bronchus; TB, terminal bronchus; RB, respiratory bronchiole; AD, alveolar duct; AS, alveolar sac; Al, alveolus. Transmission electron micrographs of the lungs of C. gambianus (C) and C. foxi (D) showing the epithelium that lines the terminal bronchus (TB). Boxed areas, ciliated epithelial cells; CC, Clara (serous) cells; BM, basement membrane; Co, collagen fibers; Er, erythrocytes; Al, alveolus; BC, blood capillary. Transmission electron micrographs of the lung of C. gambianus (E) and that of C. foxi (F) showing interalveolar septa that separate the alveoli (Al). The blood capillaries (BC) which contain erythrocytes (Er) are found in the interalveolar septa. Arrows, collagen fibres. The insert on Fig. 3F shows a double capillary system, where blood capillaries (BC) are exposed to air only on one side (dashed ‘boxed’ area) and a single capillary one where blood capillaries are exposed to air on both sides of the interalveolar septum (circle) of the parenchyma (gas exchange tissue) of the lung of C. foxi. Er, erythrocytes contained in the blood capillaries; Al, alveoli; asterisk, a type-II (granular) pneumocyte.