Growth. A Study of Johnny and Jimmy. By Myrtle B. McGraw, Ph.D., Research Psychologist and Assistant Director of the Normal Child Development Clinic, Neurological Institute, Columbia Medical Center. With a Preface by Dr. Frederick Tilney and an Introduction by John Dewey. Drawings by Kenneth W. Breeze. Published by  D. Appleton-Century Co., Inc., New York, London. Pp.  319, including References and Index. Illustrated. $3.50.

This study of the first two years of the development of Johnny and Jimmy is a work of very great importance in several particulars. In the first place, it might be said that on the theory that Johnny and Jimmy are identical twins, which is open to some doubt, the presumption of identity of such twins receives a considerable shock as a result of the development of these two personalities. In fact one is impressed by the possibility that the whole concept of the identity of monozygotic twins is somewhat of a myth and is dependent upon a lack of the care and detailed study of their individual characteristics such as the present work exemplifies.

The work was planned primarily for the purpose of the study in two identical twins of the effect of different types of experience upon the development of certain skills. Did practice result in greater speed of development ? Were the results of practice in one field carried over to another, and was there a difference of results in the two twins? These are usual sorts of problems. The main difference in the way in which they were studied, however, was that instead of the usual method, which takes as it were samplings of conduct from various chronological periods and endeavors to put them together in some sort of coherent whole, these children were studied as wholes from the very beginning. The separate skills were studied as expressions of the entire personality as far as that was possible. And so we have as a result not isolated observations but a coherent picture of development and integration going along hand in