none Antennal development of Bracon hebetor (Say) was examined at a cellular and ultrastructural level. Imaginal buds from parthenogenetically produced male larvae of known age were examined by dissection, light microscopy, and transmission and scanning electron microscopy. The adult male antenna consists of 18-20 cylindrical flagellar segments with proximal scape and pedicel. In the 56- to 60-h-old larva, the antennal bud is an undifferentiated, ovoid cellular mass. By 92-96 h, the bud has developed into an elongated, tubular, fully segmented appendage. Cell death, uniformly distributed in the bud, occurs at a low level throughout the 40 h but does not appear to have a major morphogenetic role. Cell size remains constant throughout the 40 h. A high level of mitotic activity is responsible for growth of the bud. A peak in mitosis is detected between 72 and 76 h, just before segmentation. Segments appear to be formed synchronously. Segmentation does not appear to involve localized zones of proliferation, or cell death, or statistically significant changes in cell size. Alterations in cellular interactions with resultant shifts in cell shape or position may be involved.