(1.) The reconstruction of an organism from a knowledge of some only of its parts is a problem which has occupied the attention of biologists for many years past. Cuvier was the first to introduce in his Discours sur les Révolutions de la Surface du Globe,’ 1812, the idea of correlation. He considered that a knowledge of the size of a shoulder blade, leg, or arm might make it possible to reconstruct the whole individual to which the bone had belonged. The conception was taken up by Owen, but has fallen into discredit owing to the many errors made in attempts from a wide but only qualitative knowledge of the skeleton, to reconstruct forms the appreciation of which depends really on quantitative measurement and an elaborate quantitative theory. Such a theory having now been developed, and anatomists having provided large series of measurements, it has become possible to reconsider the problem on a sounder basis, and to determine more closely the limits under which our modern methods may be safely applied. The three fundamental problems of the subject are: (i.) The reconstruction of an individual, of whom one or more organs only are known, when a series of organs for individuals of the same local race have been measured and correlated.