Date of Award


Degree Type


Degree Name

Doctor of Philosophy


A basic problem in insect metamorphosis is the means by which insects change shape. This can be studied by examining the shape changes of individual epidermal cells. I have found that removal of the basal lamina from the epidermis allows the shape and basal surfaces of these cells to be seen by scanning electron microscopy. In the 5th larval stage of Calpodes ethlius the cells extend basal processes or feet. Feet develop in three phases. Just after ecdysis they are short and randomly oriented. The cells are closely packed and their bases have punctate hemidesmosomes. The hemidesmosomes become elongated and axially oriented before commitment to pupation. The feet then also extend, and orient axially. The feet contract late in the stadium, disappearing as the cells move to their pupal positions. This cell rearrangement is facilitated by the formation of wide intercellular lymph spaces. Filopodia span and presumably aid closure of the spaces between the cells at pupation. The changes in the feet suggest that they are prime movers in epidermal morphogenesis.;The disposition of the cytoskeleton is related to the control of cell shape. For example, orientation of the feet may be controlled by selective stabilization of dynamically unstable microtubules. My work on epidermal cells suggests that cytoskeletal shape may also be influenced by somatic inheritance. The cells contain apical bundles of F-actin (shown using rhodaminyl phalloin labeling) which survive for about 36 hours after the 4th-5th larval ecdysis and associate with a transverse cuticle component. The number of bundles is paired in adjacent cells which are presumed to be siblings. The maintenance of cytoplasmic continuity through midbodies connecting siblings may preserve the paired patterns. These patterns are a result of sibling similarity, either in ploidy or by the inheritance of transient determinants for bundle pattern and position.;I have found that the secretory cell of the dermal gland is another epidermal cell whose shape is partly determined by the arrangement of its microfilament skeleton. The cell is distended during the intermoult by accumulation of secretion in vacuoles encapsulated by F-actin. At ecdysis the microfilament capsules collapse while the secretion is discharged and the cell shrivels. The microfilaments form into storage bundles which are then redistributed into capsules. This cycle repeats in each stadium until the cell atrophies in the pupa.



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