Evidence for the existence of a concentration gradient in the segments ofGalleria mellonella and ofRhodnius prolixus has been reported elsewhere. InGalleria it is possible to determine the functional form of the gradient by measuring the deviation of the scales from their normal direction after the transplantation of a piece of the intersegmental integument from the anterior or the posterior margin into the segment. The calculated values indicate the "force" with which the scales are oriented in an axial direction. This "force" corresponds to the slope of the concentration gradient.Different curves are found for the forces depending on the origin of the graft (anterior or posterior margin). This seems to be the result of unequal shrinking of the grafts. The geometrical mean of the average of the forces for anterior grafts and that for posterior grafts is nearly constant all over the segment (only the parts near the segment margins could not be included in the measurement). Thus the concentration gradient declines almost linearly. Linearly declining concentrations are expected between two different but constant concentrations which may be assumed to be located in the anterior and the posterior margin of the segment.