Fig. 8

Morphogenesis of the canaliculus in secretory cells during the second half of pupal development. Cryosections through hypopharyngeal glands at various developmental stages were labeled with phalloidin and imaged by confocal serial sectioning. a-f Maximum intensity projections of image stacks. g-l Individual optical sections at a higher magnification. a and g At P5, the F-actin tube, representing F-actin associated with the developing canaliculus, is thin and short with a narrow lumen. b and h In developmentally more advanced P5 specimens, the F-actin tube has increased in length and diameter. As a result of periodic constrictions, the tube resembles a series of oblate spheroids on a string. c and i At P6, a dense web of F-actin (asterisk) forms an expanded tube of uniform diameter. d-f and j-l Between P7 and eclosion of the worker bees, F-actin in the tube becomes reorganized and concentrated into rings. Ring distance increases during developmental progression, whereas the number of interconnections (arrowheads) and the amount of F-actin in association with the inter-ring segments decreases. Bars, a-f 5 μm; g-l 2.5 μm