1. The size of the respiratory surface of larval tracheal gills in Limnephilini depends on both the size and the number of gills. The size of the tracheal gills in related to the larval body size, whereas the number of the tracheal gills is determined by the different environmental oxygen concentration. 2. The oxygen consumption of the larvae is a function of the oxygen concentration in the water. Therefore, the adaptation to environmental oxygen depends on the number of tracheal gills as well as on conformity of the larvae in oxygen metabolism.