Figure 1

Pictures taken through a light microscope (LM). At top left – entire, intact hornet. At top right – hornet in dorsal aspect, with the cuticle of its tergites removed from the first three segments of the gaster. One can see two empty spaces (formerly housing two air sacs) and between them – a hard partition – the mediastinum (M) that ends with a diaphragm (D). Only in the terminal third-quarter of the gaster, beyond the walls of the air sacs, do internal organs fully occupy all available space. At bottom left, showing hornet in dorsal aspect, we have retained a strip of cuticle but where the cuticle has been removed (arrows), one can see the white wall of the air sacs. At bottom right, the right half of the gaster has been removed by scissors, leaving only the partition separating between the two air sacs (i.e., the mediastinum) and also the left air sac. For details see Results section.