Figure 4

Figs. a–e were photographed using SEM; Fig. f is a schematic drawing. Fig. a, the view outside the air sacs and the aperture (AP) of large trachea. Bar = 100 μm. Fig. b, large trachea (TR) emerging from an air sac. Bar = 100 μm. Fig. c, the intersegmental conjunctive (IC), i.e the membrane which overlies part of the next segment, which starts underneath it. HY indicates the hypocuticle. Bar = 100 μm. Fig. d, enlargement of the braid of tracheae, which pass to the intersegmental conjunctive (IC of Fig. c). TRB tracheal branches, EP = epithel covering the braid of tracheae, TS = transverse stripes. Bar = 100 μm. Fig. e, details of the peripheral photoreceptors (PP's) in the yellow region of the gastral segments. The PP's are evident, each of them surrounded by a branch of a trachea (TR). Bar = 1 μm. Fig. f, scheme of the main structures featured in the previous parts of this plate: The general configuration fits that of the picture in Fig. c. One can see that a yellow stripe from the gaster of a hornet on its interior surface (1) has on its brown side tracheae connecting to the preceding segments (2) and also tracheal connections to the exterior (3), as well as one (or two) large air sac/s in the segment (4) from which emerge braids of tracheae to the IC region (5), where they split into thinner tracheae (6); the latter pass into the PP (7). Thin layers of cuticle seal the PP from underneath, but the layers are rather transparent and thin (8). In this region there is yellow pigment around the PP (9) and numerous cuticular layers extending towards the exterior (10), as well as a layer of epicuticle (11). 'A' indicates the upper part of the cuticle, where each PP has a light-admitting canal which is blocked only by a thin layer of epicuticle (11). The inner layer of the cuticle is the hypocuticle (12).