The determination of polarity in the developing insect retina.

The retina in Oncopeltus fasciatus is a polarized structure in which all ommatidia are orientated the same way. By a series of grafting experiments we have shown that the orientation of ommatidia is partly dependent upon the orientation of the epidermis from which they develop and partly on the orientation of the host eye. Grafts which invert the forsoventral axis of the presumptive eye epidermis do not disrupt the orientation of the nascent ommatidia. Grafts which are rotated by 90 degrees or 180 degrees produce altered patterns of orientation. The polarity of the epidermis is to some extent conserved in these cases. Significantly ommatidia at the graft/host border take up orientations intermediate between the extremes found in the graft and host. Small rotated grafts assume the polarity of the host retina. These results are compared with the effects of similar grafts on developing insect bristle patterns.