The question that arises is: which, if any, of the linear dimensions is correlated with general size? Amadon (1943) has made a cogent plea for the recording of weights in the routine examination of bird specimens, because “we cannot fully evaluate the biological significance of geographical variation in measurements of appendages without first relating these measurements to general size.” An attempt to use the dimensions “body length” obtained by subtracting “tail length” from “length of skin” was fruitless because of the variation in methods of taxidermy, and because of the smallness of the differences involved. When mean values for each dimension are plotted graphically against each race (the method used by Miller, 1941) some Fig. 18—Clines in wing length in races of Petroica (Miro) australis (Spar.). general correlations are evident, but it is impossible to tell by inspection whether such correlations are isometric or allometric. The most satisfactory method of demonstrating the relationship between the size of one organ and that of another in a related group of races is by plotting the information on a double logarithmic graph when, if the points for several different forms fall on a straight line “curve,” a constant growth rate (in this case phylogenetic and not ontogenetic) may be inferred. If the curve slopes at an angle of 45° with abscissa and ordinate, the relationship between the two organs is isometric—i.e., change in one is in direct proportion to change in the other, but if the slope of the curve is at any other angle, the relationship is allometric—i.e., changes are differential. Allometry between adults of different races, implying phylogenetic, rather than ontogenetic changes, is known as allomorphy (Huxley, Needham and Lerner, 1941) or heteragony.