In the present investigation, oxygen consumption of skeletal muscle and of liver from B. boreas and B. woodhousei was measured in vitro. Skeletal muscle was chosen for study because this tissue comprises a large proportion of the body mass, and because metabolic responses of muscle tissue to temperature can be expected to parallel those of intact animals (Rieck, Belli, and Blaskovics 1960; Bishop and Gordon 1967). Liver was selected for study because of the relatively large size of this organ and because of its primary role in intermediary metabolism. The objective of the study was (1) to test the hypothesis that these species of toads have diverged physiologically in consequence of evolutionary temperature compensation, and (2) to [...]