Fig. 1. Location and size of spiracle openings in the fruit fly Drosophila melanogaster. (A) sp1, mesothoracic spiracle; sp2, metathoracic spiracle; sp3–9, abdominal spiracles. (B) Scanning electron microscopic image of Drosophila shows the position of the anterior spiracle sp1 between propleura and mesopleura. The posterior spiracle sp2 is located between the basis of the haltere and the mesomera. In Drosophila the prothoracic spiracle is reduced. (C,D) Shape and size of the spiracle opening area of sp1 and sp2, respectively. Red shading approximately indicates measured spiracle opening area. The metathoracic spiracle opening area is approximately 26% larger than the mesothoracic spiracle opening area. Values are means ± s.d., N=10 flies.