picked up in order to be utilized by those acquainted with this method of interpretation.... If the signs of the times are now read correctly, the most striking advance in scientific methods of thinking during the present century will be in the direction of interpretation from the standpoint of processes--dynamically.” For these reasons I have begun the list of literature with certain references which deal with the dynamic relations of the environment. These publications are particularly valuable not only for this method of treatment, but also for their content. These papers clearly emphasize the “orderly sequence of external nature,” a conception which must be grasped much more than superficially, if one is to interpret the development or evolution of environments. Although this is an essential part of our problem, as has been so well expressed by Brooks, yet this phase is probably one of the least understood by zoölogists. And as long as zoölogical students lack the proper training this condition will continue. To neglect this aspect in the training of an ecologist is like neglect of chemical training in a physiologist or of a physiological training in a psychologist. For one who is ignorant of the principles of “orderly sequence,” or successions of changes occurring in the physical, vegetational, and animal environments, it is manifestly impossible to realize their development; and the application of such principles to the interpretation of practical problems is utterly beyond his grasp. We are thus able to see that although the phrase “orderly sequence of external nature” is fundamentally a simple conception, it is not grasped without effort, training, and careful investigation. Obviously it is impossible to arrange the series of references with perfect satisfaction. The arrangement which will serve one purpose will not another, and for this reason it has been necessary to arrange the lists in more than one order. Certain general references, or some intended to facilitate the acquirement of the general _point of view_, are given first, and others are arranged alphabetically. For example, the papers listed on the processes of change in the physical and vegetational environment are approximately in an order in which they may profitably be studied to make the view as concrete as possible. It is primarily not the abstract idea of the principle of change, which is relatively easy to grasp, but to be able to apply it to any condition or location and to make it a guiding principle is very difficult. And judging from my own observation upon others and my own experience this method is very rarely mastered, if at all, unless it is actually worked out in some concrete case, and later expanded to its logical consequences.