|Select image to enlarge in new window||Tracheal System pages 18-19 | 20-21 | 22 | 23
The larval tracheal tree originates from a series of
placodes that, projected on the blastoderm (stage 5), map to the dorsal ectoderm.
Segments T2 through A8 each gives rise to one pair of tracheal placodes
(Poulson 1950; Campos-Ortega and Hartenstein 1985; see Manning and Krasnow,
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During stage 12, the invaginated tracheal pits elongate and form a dorsal and a ventral stem. The ventral stem bifurcates into a posterior branch (4) and an anterior branch (5), The dorsal stem gives (1) off two side branches: one toward the anterior (2) and the other toward the interior of the embryo (3), (A1, A8) Abdominal segment 1, 8; (as) anterior spiracle; (DEA) dorsal ectoderm; (ms) mesoderm; (T1) thoracic segment 1; (VNE) ventral neurogenic region.