The spiracle of the seventh segment has been moved forward to a more anterior position in the segment. The ninth segment is highly modified and bears a large dorsal plate that extends to become a narrow band running beneath the anus. The tenth segment is a pair of sclerotized plates flanking the anus. The dorsal ventral patterning of the thorax is regulated by the dorsal-ventral polarity system and segmentational patterning regulated by gap , pair rule and segment polarity genes. The two transcripts of Antennapedia take on different roles in ectoderm and endoderm and in the three thoracic segments.
Ultrabithorax expression spans the last thoracic and first abdominal segments.
It should be kept in mind that the adult thorax is derived from the wing imaginal disc and leg discs, while the adult abdomen has a completely different embryological origin, being derived from nests of histoblasts held in the embryonic and larval epidermis. Seven gene systems are involved in the most posterior adult segments. Tailless regulates the posterior stripes of even skipped and fushi tarazu , which in turn regulate the segment polarity genes. The second gene system regulating tail morphogenesis is the posterior group genes of the terminal system. Inhibition of Hunchback translation by Nanos allows for the expression of caudal , important for the last two abdominal segments and the telson.