Imaginal Disks and the Abdominal Histoblasts of Calliphora erythrocephala (Diptera)

Abstract

SINCE 1946 imaginal disks of Drosophila have been subjects for experimental morphogenesis³ because of their morphological discreteness, the long period they remain undifferentiated in the larva, and the ease of operation and transplantation. All the adult epidermal structures of cyclorrhaphous Diptera are thought to derive from imaginal disks: head structures from labial, antennal, and eye disks; limbs, wings, and general thoracic epidermis from thoracic disks; genital apparatus from genital disks; and the abdominal epidermis from abdominal “imaginal disks”⁴ which, however, have been ignored because they differ from other imaginal disks. The adult cells of disks are set apart from the larval epidermis during embryonic development. Earlier workers have suggested a larval⁵ and prepupal⁶ origin of the abdominal “disks” in other species. Bautz⁷, in a study of the larval abdominal epidermis of Calliphora, shows that the “disks” are probably present from the time of hatching also. I have examined the abdominal epidermis of Calliphora erythrocephala throughout larval life, in whole mounts and in sectioned material by light and electron microscopy. Observations on the abdominal histoblasts show they should no longer be referred to as “imaginal disks”, because the abdominal histoblasts differ not only in morphology but also in ultrastructural differentiation and developmental behaviour.