The retina in Oncopeltus fasciatus is a polarized structure in which all ommatidia areorientated the same way. By a series of grafting experiments we have shown that the orienta-tion of ommatidia is partly dependent upon the orientation of the epidermis from whichthey develop and partly on the orientation of the host eye. Grafts which invert the dorso-ventral axis of the presumptive eye epidermis do not disrupt the orientation of the nascentommatidia. Grafts which are rotated by 90° or 180° produce altered patterns of orientation. The polarity of the epidermis is to some extent conserved in these cases. Significantlyommatidia at the graft/host border take up orientations intermediate between the extremesfound in the graft and host. Small rotated grafts assume the polarity of the host retina. Theseresults are compared with the effects of similar grafts on developing insect bristle patterns.
