Further analysis of the results proves that this statement is not true. When the averages for the two sexes are compared, it appears that the males learned much less quickly at four months than at one month, whereas just the reverse is true of the females. The dash and dot line of the figure extends from the index of modifiability of the one-month males (72) to that of the four-month males (120); and the regularly interrupted line similarly joins the indices of the one-month (104) and the four-month (85) females. In seeking to discover age differences in docility or ability to profit by experience we have stumbled upon what appears to be an important sex difference. Perhaps I should add to this presentation of partial results the following statement. Since there are only four individuals in the four-month group, two of each sex, the indices are not very reliable, and consequently too much stress should not be laid upon the age and sex differences which are indicated. In view of this impressive instance of the way in which averages may conceal facts and lead the observer to false inferences, I wish to remark that my study of the dancer has convinced me of the profound truth of the statement that the biologist, whether he be psychologist, anthropologist, physiologist, or morphologist, should work with the organic individual and should first of all deal with his results as individual results. Averages have their place and value, but to mass data before their individual significance has been carefully sought out is to conceal or distort their meaning. Too many of us, in our eagerness for quantitative results and in our desire to obtain averages which shall justify general statements, get the cart before the horse. Figure 33 presents the beginning of what I propose to call plasticity curves. When these three curves are completed on the basis of experiments with five dancers of each sex for each of the ages indicated on the base line of the figure, they will indicate what general changes in plasticity, modifiability of behavior, or ability to learn (for all of these expressions have been used to designate much the same capacity of the organism) occur from the first month to the nineteenth in the male and the female dancer, and in the race without respect to sex. So far as I know, data for the construction of plasticity curves such as I hope in the near future to be able to present for the dancing mouse have not been obtained for any mammal. At present it would be hazardous for me to attempt to state any general conclusion concerning the relation of docility to age.