This project is concerned with physiological aspects of altitude, particulary as they act to limit the range of or isolate populations and species of animals. It has now run through the summer of 1955, 1956, and 1957. The results of the studies of the first two summers have been summarized in a paper which is being published in the October 1957 issue of Physiological Zoology. The work of this report dealt primarily with the effect of differneces in altitude on the rate of oxygen uptake in two species of arthropods and has been summarized in previous reports. Project Number 79.