III. Contributions to the mathematical theory of evolution

1. If a series of measurements, physical, biological, anthropological, or economical, not of the same object, but of a group of objects of the same type or family, be made, and a curve be constructed by plotting up the number of times the measurements fall within a given small unit of range to the range, this curve may be termed afrequency curve . As a rule this frequency curve takes the well known form of the curve of errors, and such a curve may be termed anormal frequency curve . The latter curve is symmetrical about its maximum ordinate. Occasionally, however, frequency curves do not take the normal form, and are then generally, but not necessarily, asymmetrical.