In prophylaxis of the family the first indication is to stop the production of degenerates. Two measures have attracted considerable attention, and from their seeming simplicity have met with much favour. The first is regulation of marriage. This, as a means of preventing degeneracy, has been much over-estimated. Laws claiming to regulate marriage have ignored two factors. In the first place the graver degeneracies only are taken into account. From what has been shown as regards the tendency of the degenerate to intermarry, and from the fact that restraints on marriage inevitably result in illicit relationships of permanent character (equally productive of degenerates whose defects have been increased by the condition in which they are born), the only procedure likely to be of value in this relation is to regard marriage simply as a contract designed for certain ends and permit its annulment for fraud, for concealment of defects (intentionally or otherwise) incompatible with the procreation of healthy children. In its essence this is the English common law theory. Its principle is recognised by the divorce codes of various continental European countries. Furthermore, it is on this principle that the Pope not infrequently annuls marriages, divorce not being recognised by the Church of which he is the head. It is certainly best for the stability of the family that unhealthy unions should have the least permanency possible. Another element in prophylaxis, castration, ignores completely the rights of individuals under the English common law (and, so far as the United States is concerned, a provision of its constitution). Although sacrificing these important guards against that degeneracy in the body politic which inevitably reflects itself in degeneracy in the individual, this procedure fails to accomplish its end, since it ignores completely the principle of transformation in heredity. The distance between the criminals (whom it is proposed to castrate) and the hysteric offspring of good family is not so great that the progeny of one will not be as degenerate as the progeny of the other. Whatever may be said of the value of this procedure as a deterrent, its use as a prophylactic is comparatively small.