Only a few references are given on general physiology, metabolism, and allied subjects, but those given furnish a valuable index to further literature. Only the most arbitrary line can be drawn between papers dealing with habits, behavior, and individual ecology, and for this reason most of the references selected are arranged alphabetically. Particular attention should be called to the fact that it is not to be assumed that the various authors strive to make the points to which attention is here called; they may or may not do so. My aim is to call attention to the _utility_ of the publications from the _standpoint_ advocated throughout the book. From this point onward in this book the references form its main feature. For this reason it is important that one should not get an exaggerated idea of the value of the literature. It is perhaps true that a large part of the best ecological work has been done with little knowledge of other ecological writings. This was of course particularly true of the early workers, and the best work of to-day does not come from the largest library centers. A student looking over these lists, and finding that he has access to relatively few papers, may conclude that all effort is of no avail. The greatest need is not all or even a majority of the publications on the _general field_, but the relatively limited number which bear directly upon the problem at hand and enough of the general papers to aid him in a general orientation. It may be of some comfort to the isolated student, with his small shelf of books, to realize that there are perhaps not a half-dozen libraries in America which contain _all_ the references given in this book. The nearer one reaches the boundaries of our knowledge, the smaller the amount, and often the smaller the value of the literature, and the greater the value of a proper orientation, which comes only with a grasp of general principles. * * * * * (The laws of physical and vegetational changes and their influence upon animals. The dynamic or process relation of the environment.) BANCROFT, W. D. 1911. A Universal Law. Science, N. S., Vol. XXX, pp. 159-179. The law of adjustment or response to strain. A very important paper viewed from the dynamic and process standpoint. HENDERSON, L. J. 1913. The Fitness of the Environment. An Enquiry into the Biological Significance of the Properties of Matter, pp. 317. New York. The Macmillan Company. Valuable ecologically because of its exposition of the orderly sequence and _regulatory_ character of physico-chemical and physiological processes, and the application of chemical equilibria and the Phase Rule to metabolic changes. He says, “Now there can be no doubt that, when feasible, the ideal method--from the physico-chemical point of view--to describe a material system is in terms of the phase rule.” p. 260. CHAMBERLIN, T. C., and SALISBURY, R. D.