During the last fifteen years these studies have been carried on with great activity. It seemed, therefore, that the time had come for a short and comprehensive review of their present condition. Such a review of a young and rapidly growing science cannot be expected to reveal any final conclusions; yet by bringing together very various material from many lands, it serves to show us how we stand, to indicate the progress already made, and the nature of the path ahead. In these matters we in England have of recent years fallen far behind; no book, scarcely a solitary magazine article, dealing with this matter has appeared among us. It seemed worth while to arouse interest in problems which are of personal concern to every citizen, problems which are indeed the concern of every person who cares about the reasonable organisation of social life. I would willingly have given the task to abler hands. But I found no one in England who was acquainted with the present aspects of these questions, and was compelled, therefore, after considerable hesitation, to undertake a task which had long appealed to me from various sides, medical, anthropological, and social. There is, I believe, nothing original in this book. It simply represents a very large body of intelligent opinion in many countries. I have to acknowledge with gratitude the assistance, always ungrudgingly rendered, which I have received from very many directions. I would specially mention those medical officers of prisons in Great Britain who answered my Questions issued at the beginning of 1889, Dr. Hamilton Wey of the Elmira Reformatory, Dr. Vans Clark, formerly Governor of Woking Prison, Professor Lombroso of Turin, Dr. Antonio Marro, the Rev. J. W. Horsley, Dr. Langdon Down, Dr. Hack Tuke, Dr. Francis Warner, etc. It would, however, be impossible to enumerate all those to whom I am indebted. In such a task as this the writer himself has the smallest part; the chief shares belong to an innumerable company of workers, known and unknown. H. E. THE CRIMINAL. CHAPTER I. INTRODUCTION. Of criminals, actual or nominal, there are many kinds. It is necessary, first of all, to enumerate the chief varieties.