Legend: At the end of germ-band retraction [stage 13] the branched tracheal invaginations of all segments fuse and lay down the basic pattern of the larval tracheal tree. [1] The dorsal stems of the invaginations develop into the transverse connectives (tc; nomenclature after Keilin 1944; Whitten 1980). [2] The anteriorly directed dorsal branches of all segments fuse into the dorsal longitudinal tracheal trunks (dlt). [3] The interiorly directed branches form the tracheae of the intestine (it). The first (T2) and last (A8) tracheal invaginations differ in their development from the remaining ones. The first invagination remains open to the outside and forms the anterior spiracle (as). It gives off several additional branches that tracheate T1 (tT1), the gnathal segments (tg), the pharynx, and the brain (dorsal cervical trachea, dct), The tracheal invagination of A8 has fused with the placode of the posterior spiracle (ps) during previous stages.

During stage 15, the ventral anterior and posterior branches [4, 5] fuse into the lateral longitudinal trunk (llt). The tips of the former dorsal stem [6] and side-branches of the posterior ventral branch [4] continue to elongate toward the midplane. They form the dorsal tracheae (dt) and ventral ganglionic tracheae (vgt), respectively. The latter tracheae grow right over the dorsal surface of the ventral nerve cord. Corresponding dorsal tracheae and ventral ganglionic tracheae of either side are connected by thin anastomoses.

The drawing of a stage 17 embryo shows the main components of the fully developed early larval tracheal tree. For a more detailed depiction of the late embryonic tracheal tree, see Manning and Krasnow, this volume. (mg) Midgut; (mp) Malpighian tubules; (mu) somatic musculature; (myo) myoblasts; (pn) peripheral nerve.