Morphogenesis of the antenna of the male silkmoth, Antheraea polyphemus. IV. Segmentation and branch formation.

The imaginal antenna of the male silkmoth Antheraea polyphemus is a featherlike structure; its flagellum consists of about 30 stem segments each giving off two pairs of side branches. The antenna develops during the pupal stage (lasting in total about 21 days) from a leaf-shaped anlage by incisions proceeding from the periphery towards the prospective antennal stem. Primary incisions, starting about 3 days after apolysis, form double branches, which arethen split into single branches by parallel running secondary incisions. The initial pattern of tracheae and peripheral nerves is completely rearranged during these morphogenetic processes which are finished 9-10 days after apolysis. In Antheraea the dorsal and ventral epithelial monolayers of the antennal anlage are successively subdivided during development into a pattern of repetitive epithelial zones. Within the first day after apolysis alternating stripes of sensillogenic and non-sensillogenic epithelium are differentiating. Then the latter are further subdivided, and at last four different stripelike zones (I-IV) can be discriminated. Long basal protrusions of the epidermal cells ('epidermal feet'), and most probably haemocytes, seem to be involved in the reconstruction of the epithelium: both show characteristic arrangements within the antennal anlage during successive developmental stages.