Larval-adult oviduct transformation in an insect (Oncopeltus fasciatus): cytological study

The lateral oviducts of the milkweed bug undergo a drastic larval-adult transformation during the last larval instar. This transformation is hormonally regulated and is connected with considerable morphological and cytological reorganization. Prior to transformation, the ducts are long and thin. The epithelial cells are fusiform with their long axes running cranial-caudal. They are tilted and slightly helically arranged. During transformation, the lateral oviducts shorten dramatically, the cells become columnar, and their long axes shift into the plane of cross sections. Whereas the cells appear cytologically uniform in the larval state, after transformation, the lateral oviducts are divided into a cranial secretory part, and a caudal part which exhibits a cuticular lining. Secretory processes and deposition of the cuticle start in the larva, immediately after transformation. Cuticle synthesis is first observed next to the common oviduct and progresses craniad. The cuticle-lined luminal surface reveals circular ridges and an intricate pattern of cteniform spines which are directed caudally. The novel mode of cell rearrangement during oviducal transformation and the functional significance of the two parts of the adult lateral oviducts are discussed.