Fig. 9. Horizontal semithin sections of the first abdominal segment/posterior thorax in D. hydei. (A) Section just below the first abdominal tergite, showing the heart chamber (H1) with first ostia (O1) and venous channel (VC) bordered by a cuticular septum (CS), pericardial diaphragm (PD) and constitutive fat tissue (CFB). (B) Section 32 µm below A, showing the venous channel and the tergo-pleural muscle (M) attached to the cuticular septum. (C) Section 30 µm below B. The aorta (Ao) is collapsed. The venous hemolymph channel is bordered by the tergo-pleural muscle. (D) Tubular tergo-pleural muscle. Detail similar to C. (E) Section 180 µm below B at the basis of the haltere (Ha). (F) Section 268 µm below B. Venous channel above the metathoracic spiracle (Sp II). The tergo-pleural muscle (M) is close near the pleural septum (PS), where it is attached 98 µm more ventrally. FB, fat body; I, intestine; Ph II, mesophragma; T, trachea.