LUNG ULTRASTRUCTURE AND THE SURFACTANT-LIKE SYSTEM OF THE CENTRAL NETTED DRAGON, CTENOPHORUS-NUCHALIS

We have examined the ultrastructure of the unicameral lung of the cent ral netted dragon, Ctenophorus nuchalis, using light, scanning electro n, and transmission electron microscopy. The inside of the outer wall of the saccular lung were oriented perpendicularly to the wall. On the luminal side, the openings of the faveoli were connected by a network of smooth muscle bundles (trabeculae). Whereas the faveoli are 10 to 100 times larger than alveoli from similarly sized mammals, we previou sly found that the amount of surfactant-like material which can be lav aged from these lungs is about 70 times greater per surface area of lu ng than that from a similar sized mammal. The lungs of C. nuchalis con tained very large numbers of alveolar type II cells, often located in groups, and sometimes apparently stratified. Each cell contained many lamellar bodies in its cytoplasm. A number of different forms of extra cellular surfactant, including the distinctive, cross-hatched appearin g, tubular myelin, were apparent in the airspaces. During deflation, t he walls of the faveoli fold in a concertina fashion between the outer wall of the lung and the apparently more rigid primary trabecular net work. Large amounts of extracellular surfactant-like material could be seen in the corners which were so formed. This location is consistent with this material acting as an ''anti-glue'' in the lizard lungs, fa cilitating the unfolding of the epithelial linings during inflation. T he large number of cilia and their position is consistent with a clean ing function in which surfactant may also be involved.