The families of 558 insane persons cared for in the London county asylums were investigated, and, according to reports received from the educational authorities, only 15 of these (less than 3 per cent) had mentally defective children. As to the time of the birth of the children, whether before or after the attack of the insanity, we find the following figures: 56 out of 573 parents had children after their first attack of insanity, and 106 children were born after the onset of insanity in the parent; while the remaining 1259 children were born before the parent became insane. Altogether, as will be seen from a discussion of the various factors rendering marriage permissible or nonpermissible, I am inclined to consider environment a more important factor than heredity. The purely physical characteristics bear the indelible impress of heredity. But the moral and cultural characteristics, which in the modern civilized man are much more important than the physical, are almost exclusively the results of environment. =Neuroses--Neurasthenia--Psychasthenia--Neuropathy--Psychopathy= I will not attempt either exhaustive or concise definitions of the terms named in the caption, for the simple reason that it is impossible to give satisfactory definitions of them. The conditions which these terms designate do not constitute definite disease-entities, and many different things are understood by different people when these terms are mentioned. Only brief indications of the meaning will be given. Neurosis is a functional disease of the nervous system. Neurasthenia is a condition of nervous exhaustion, brought about by various causes, such as overwork, worry, fright, sexual excesses, sexual abstinence, and so on. The basis of neurasthenia, however, is often or even generally a hereditary taint, a nervous weakness inherited from the parents. Psychasthenia is a neurosis or psychoneurosis similar to neurasthenia, characterized by an exhaustion of the nervous system, also by weakness of the will, overscrupulousness, fear, and a feeling of the _unreality_ of things. Neuropathy is a disease or disorder of the nervous system. Psychopathy is a disease or disorder of the mind. Of late years we often hear people referred to as neurotics, neurasthenics, psychasthenics, neuropaths or psychopaths. These are undoubtedly abnormal conditions, and, taken as a general thing, they are dysgenic factors.