hypothesis would be permissible; but it is an offence against the principles of scientific method to invoke its aid, before we have exhausted the possibilities of explanation offered by well-known existents and forces. That certainly has not yet been done, and the upholders of the doctrine have hardly made any attempt to justify it in this the only possible manner in which it could be justified. The only evidence of this sort adduced by Espinas is the rapid spread of a common emotion and impulse throughout the members of animal and human groups; and of such phenomenon we have already found a sufficient explanation in those special adaptations of the instincts of all gregarious creatures which are unmistakably implied by the way in which the expression of an emotion directly evokes a display of the same emotion in any onlooking member of the species. We may, then, set aside the conception of a ‘collective consciousness’ as a hypothesis to be held in reserve until the study of group life reveal phenomena that cannot be explained without its aid. For it may be confidently asserted that up to the present time no such evidence of a ‘collective consciousness’ has been brought forward, and that there is no possibility of any such evidence being obtained before the principles of social psychology have been applied far more thoroughly than has yet been done to the explanation of the course of history. In adopting a so far unsympathetic attitude towards this doctrine, we ought to admit that, if there be any truth in it, the ‘collective consciousness’ of even the most highly organised society may be still in a rudimentary stage, and that it may continue to gain in effectiveness and organisation with the further evolution of the society in question. After this digression we may return to the consideration of the emotional characteristics of simple crowds. We have to notice not only that the emotions of crowds are apt to be excessively strong, but also that certain types of emotion are more apt than others to spread through a crowd, namely the coarser simpler emotions and those which do not imply the existence of developed and refined sentiments. For many of the individuals of most crowds will be incapable of the more subtle complex emotions and will be devoid of the more refined sentiments; while such sentiments as the individuals possess will be in the main more diverse in proportion to their refinement and special character; hence the chances of any crowd being homogeneous as regards these emotions and sentiments is small. Whereas the primary emotions and the coarser sentiments may be common to all the members of a crowd; any crowd is likely to be homogeneous in respect to them.