less appreciative recognition of results secured by other methods. To observe, to experiment, to reflect, to dissect, to stain, and to collect are only partial methods of investigation, and this fact should be realized and be kept in mind when estimating values and planning work. The aim of the ecologist is professedly genetic or explanatory because it is the study of _responses_ to all conditions of the complete environment. But these responses must be described, and the conditions influencing them as well, so that a descriptive aspect is an essential part in all phases of ecology. In the study of the responses of an individual, an order, or an association, pure description of the responses is necessary; but a description which will at once describe and show the working of the processes by which the results were produced, is of quite a different order. This phase of explanation has been most concisely expressed and applied by the students of the physical sciences, and biologists may profit much from a study of their methods. When, however, we turn to the viewpoint of the development of the science of ecology as a whole, a symmetrical development of the subject is most desirable. The preponderating influence of any special point of view tends, like dominance in general, to smother or suppress other germinating and competing ideas. The different special interests each have their advantages and disadvantages, as does a general interest. Diversity in students leads to diversity in the development of the subject, and a variety of emotional appeals to the student has its advantages. And just as the special student should devote some attention to the general bearing of his work, so also should the student of the general aspects cultivate some special field of interest. The preceding discussion of the aims and methods in ecological study has been intended to indicate some of its general bearings, and to give the student some idea of the tests or criteria which may be used to aid in steering his course through the maze of observations which he may make and the opinions which he encounters. It is of equal importance for the student to be able to perceive ecological relations as recorded by others, because one person’s experience is so limited compared with the general body of recorded fact and inference. Furthermore, there are also so many degrees and kinds of work that go by the name ecological, which may or may not be, and so many also which are truly ecological but which do not pass under that name, that it is necessary that the student shall be able to see through its diverse guises and recognize its essential character. Whenever the question arises as to the ecological character of a fact, inference, or conclusion, its ecological validity may be tested in the following way: Do the facts, inferences, or conclusions show a _response_ to the inorganic or organic environment: 1. As an individual of a species or kind of animal?