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The tracheal epithelium of Testudo graeca and Pseudemys scripta elegans was studied by means of light and electron microscopy, histochemistry and immunocytochemistry. Three cell types were detected by conventional light microscopy: mucous, ciliated and basal. The Grimelius silver argyrophil technique was positive in a population of tracheal cells. By immunocytochemistry, serotonin-containing cells were identified. The mucous cells of Testudo graeca contained sialomucins and sulphomucins; however, only sialomucins were detected in Pseudemys scripta elegans. By electron microscopy four cell types were observed: mucous, ciliated, basal and endocrine. Plasma cells were also found. The differences between the species studied lay mainly in the ultrastructure of the ciliated cells, the mucous granules and the presence of a special type of basal cell called 'clear basal cells' in non-hibernating specimens of Testudo graeca. During hibernation, the tracheal epithelium of Testudo graeca showed the following changes: (1) Myelin bodies were present in the cytoplasm. (2) The intercellular spaces were remarkably widened. (3) No 'clear basal cells' were present. In conclusion, the tracheal epithelium of the reptiles studied showed a pattern similar to that described in mammals but some differences from reptiles previously studied were found.

The lung of the tortoise, Testudo graeca (Chelonia) was studied by means of light and electron microscopy, histochemistry and immunocytochemistry. The lung showed the typical faviform structure of the reptilian lung. Three orders of trabeculae were observed. The epithelium of primary and secondary trabeculae was composed of ciliated, mucous, basal and endocrine cells. Mucous cells contained sialo- and sulpho-mucins and were reactive to the lectins Con-A, WGA, DBA, PNA and SBA. Endocrine cells were observed as solitary cells or forming neuroepithelial bodies. By means of immunocytochemistry, endocrine cells were demonstrated to contain serotonin. In the gas-exchange area Types I and II pneumonocytes and undifferentiated cells were observed. Free macrophages were detected in the faveolar lumen. The lung interstitium contained smooth muscle cells, fibrocytes, pigment cells, myelinated and unmyelinated nerves and intrapulmonary ganglia. Nerve terminals containing clear and dense-cored vesicles were observed in the adventitia of the blood vesicles and interspersed between the smooth muscle bands. The lung of the hibernating specimens showed a marked vacuolisation of pneumonocytes. In conclusion, the lung of Testudo graeca showed a complex histological organisation. Marked differences from mammalian lung were found.