This is an interesting and indeed important book. In a previous study the authors had shown that physical type is correlated with delinquency in general. In the present work they analyse the problem still further, and demonstrate that among delinquents, different physical types play different roles.Let me explain. Human beings, on the basis of Sheldon's painstaking studies, can be classified into four main physical types or types of body-build-endomorphs, mesomorphs, ectomorphs, and balanced types. Typical endomorphs are soft and rounded, tending to fat, with a sensitive predominance of the digestive viscera. In mesomorphs, the bones, muscles and connective tissues are predominant, the physique is heavy, hard and rectangular, and the build athletic. Ectomorphs are thin and fragile, with a relative predominance of sensory surface and of brain. Finally, the balanced types, as their name implies, are intermediate between the three divergent forms of body-build, and show no marked predominance of any particular organ-system.The various types show distinct differences in temperament. Endomorphs tend to be submissive, sensuous, relatively little interested in physical activity or adventure; mesomorphs tend to be strong and muscular, practical and active, enjoying physical activity, self-assertive and daring; ectomorphs are more sensitive and introverted, more inhibited and more prone to emotional conflict, more unconventional in ideas and outlook; and those of balanced type are less