The plethodontid or lungless salamanders breathe by means of exchange of gases through the highly vascular moist surfaces of the mouth and pharynx cavity (buccopharyngeal respiration), as well as by cutaneous respiration over the whole surface of the body which is well supplied with superficial capillaries. The evolution of the lungless salamanders coincided with the adoption of the mountain brook habitat, and it was only subsequently that they spread out into a more terrestrial type of existence (Noble, '31). The problem arose concerning whether there might be different oxygen requirements for the present land species as compared with the so-called aquatic species. Such differences if present might account for the differential distribution since both types have the same kind of mechanism for securing oxygen. A further problem was suggested from the fact that, in captivity, the salamanders frequently clump together in loosely knit groups. Salamanders have strongly thigmotactic responses and xvill crawl inside of glass bottles or under stones or sticks placed in their vicinity, and the tendency to group together may well be a manifestation of this thigmotactic response. However, it seemed worth while to determine whether such a grouping might have any effect on their oxygen consumption. It has been demonstrated that aggregation does affect the oxygen consumption of certain animals (Allee, '27). With these points of departure for experimental procedure, the problems outlined above were investigated. That relating to species requirements had been begun in 1930-31 at the American Museum of Natural History under the direction of G. K. Noble. These early experiments served to show the necessity of more perfectly controlled conditions than were available up to that time. The work was continued at the University of Chicago during the years 1932-36, with carefully controlled conditions, and only the experiments