INTRODUCTION Summarizing our information on this subject and the pertinent information to be found through the huge bibliography are not the only objectives of this chapter. An organization has been attempted which seems potentially of service in pointing out variables or factors, the study of which, through application of the experimental method, may facilitate better understanding of the various problems and encourage the formulation of new, testable hypotheses. This goal is sought by organizing the material presented around what seem to be the major aspects of realms in the variation of the environment. For the reporting of observations, the environment lends itself to measurement as variations (or duration) through space, time, and numbers, and in C. G. S., or related, units. 1 Most of the points outlined by Michael and Allen (1921) in their outline of the problems of marine ecology are covered but have been reorganized with the above variables in mind. The environmental variables delimit a form in space, time, and numbers peculiar to each species, group of species, or other biological unit being treated. For this form we shall use the term biospace, though in deference to the usual three-dimensional conception of “space” some other term might well be more appropriate for a form having more than three dimensions. Järnefelt (1940), Reijne (1948), and Detling (1951) present possible methods of illustrating these polydimensional biospaces (Fig. 16) within the restrictions imposed by two-dimensional printing. A simple sample of, or section through, a biospace would be provided by a uniformly...