Behaviour of the epidermal cell in an insect, Oncopeltus fasciatus.

The behaviour of the epidermal cell of the insect, Oncopeltus fasciatusy has been studied in the dorsal abdomen in three situations: during the moult cycle, wound healing and pattern regulation. This behaviour can be classified into seven categories: activation, division, movement, alteration in shape, death, differentiation and cuticle secretion. Data are presented on the first five categories. Aspects of cell behaviour studied during the intermoult period of the moult cycle consist mainly of activation and division. The exact stimuli for this behaviour have not been determined, although an increase in ecdysteroid titre may not be sufficient. The first mitotic figures in the moult cycle are concentrated behind the anterior border of the segment, but later the mitotic index is uniform over most of the segment. Cell behaviour induced after wounding consists largely of activation, division and movement. Degradation products from damaged epidermal cells are not solely responsible for this activation and the strongest influence appears to be the presence of an incision. Activated cells peripheral to wounds will not divide unless ecdysterone is present. Cells may divide beneath wounds and the condition required for this is probably the disruption of epidermal continuity for a minimum length of time. Cell behaviour after the confrontation of cells from different anteroposterior levels in the segment consists mainly of division and transverse elongation at the confrontation site. The intensity of this behaviour is explained by a difference in positional values between confronted cells so that there is a non-linear gradient of positional values along the segment with a discontinuity at the segment border. If this discontinuity is maintained by a special population of cells at the border, then the regeneration of segment borders can be explained by the formation of these special cells following the confrontation of cells with almost the maximum difference in positional values.