Abstract: Locke, a Canadian entomologist, recently suggested that caterpillars have evolved lungs for hemocyte gas exchange. Based on his research, the structure and function of lungs in larvae of Leucania separata and Sylepta derogata were studied by means of electron microscope and other chemical methods. The results indicated that lungs are located at the trachea of the 8th abdominal segment. Their trachea branches are taper, short and abundant, forming tracheal tufts. Through labelling hemolymph with methylene blue, we observed that the hemolymph moves backwards laterally and ventrally to flow through the 8th abdominal segment and tokus, and finally into the heart. The tracheal tufts of the 8th abdominal segment have thinner cuticle than those of the other abdominal segments, and the cuticular intima of tracheal tufts have more tubules appropriate for them to move, which are in favour of the permeation of gas. Normally these tracheal tufts have all kinds of hemocytes, which are abundant in the tufts. A large number of hemocytes released from tissues attach to the tufts by changing their structure when anoxic stress happens, which is favorable to the exchange of gas. These characteristics are similar to lungs of other higher animals, so it is concluded that this structure has the function of lung.

Key words: Leucania separata, Sylepta derogata, respiration, lungs, tracheal tufts, hemocytes, ultrastructure