The question of the existence of a criminal type is regarded as essentially anthropometrical, _i.e._, it can only be solved by the statistical analysis of a large series of measurements. Anthropometry has, of course, been used as an instrument by criminologists, but its strict application demands more than the crude contrast of mean values which is the most that has been hitherto attempted: in addition to the means, it insists that probable errors should be also calculated and recorded; that a measure of the variability of each series of measurements should be obtained; and that, in every case, effects upon measurement due to differentiation in age, stature, intelligence, &c., of the contrasted populations under measurement should be also estimated and allowed for. Having, by means of a comparison with regard to thirty-seven representative physical attributes of criminals, distinguished (1) by their conviction for different orders of crime, _e.g._, thefts, assault, arson, sexual offences, and frauds, (2) by their frequency of reconviction, and (3) by the length of their imprisonment, established the conclusion that criminals are not physically differentiated because they are criminals, but because of difference in age, stature, intelligence, &c., our author proceeds to a comparison between statistics of criminals, as a class, and of the non-criminal public. The absence of any comparative data with regard to many of the physical characters of the law-abiding classes is, of course, fatal to any precise demonstration, but a comparison of the head-length, -breadth, -height, -index, and -circumference in convicts is made with similar statistics of a set of undergraduates of Oxford, Cambridge, and Aberdeen Universities, and of the London University College Staff, with the result that prison inmates, as a whole, approximate closer in head-measurement to the Universities generally than do students of different Universities conform with each other in this regard, and that from a knowledge only of an undergraduate's cephalic measurement, a better judgment could be given as to whether he were studying at an English or Scottish University, than a prediction could be made whether he would eventually become a University Professor, or a convicted felon. Similar comparison with the general Hospital population and with soldiers (118 non-commissioned officers, and men of the Royal Engineers) establishes a similar conclusion that, so far as head-measurements are concerned, the criminal, and the hospital patient, and the soldier cannot be differentiated.