Numerous investigators have shown correhatioius between various physiological properties of aquatic organisms amidthe chuaracteristic levels of oxygemuin which the aninuals are foumud. Older studies omusurvival timuueumuder how oxygen coiuditions gemuerally imudicate that, withimu closely related groups, burrowimug species are more resistamut to oxygen deprivatiomu thamu epifaunal forms (Packard, 1905). Sinuilarly, animals living imufast-moving streanus are less resistant than those living in rela fively unnuixed pond wafer (Fox, Simmonds and Washbourn, 1935 ; Bovbjerg, 1952 ; Walshue, 1948) . Walshe ( 1948) also showed that, among the chuirononuid larvae, resistance to oxygen lack is better correlated with ecological distributiomu than with phyhogeny. Nunierous studies support the very plausible notion that animals fronu low oxygen environments have a lower rate of oxygen comusumptionthuan their counter parts from high oxygen environments when compared at the sanue oxygen concen frations. Examples are two species of Balanus (Prasada Rao and Ganapati, 1968) epifaunal and infaunal tropical echinoids (Lewis, 1968) ; oxygen minimunu layer nuysids (Childress, 1971) ; stream and pomud insect larvae (Fox, Simmonds and Washbourn, 1935) , crustaceans (Fox and Simmonds, 1933) and leeches ( Manmu, 1956) ; and maldanid polychaetes (Mangum, 1963, 1964a). Perhaps the muuost elusive physiological correlate of emuvironnuemutal oxygen level is the degree to which oxygen consunuptiomu rate is maintained constant over a range of ambient oxygen concentratiomus. It is clear that in mamuyaquatic inverte brafes respiratory regulation withimua species is not entirely constant. It varies with temperature (Thomas, 1954 ; Wiens and Armitage, 1961) , weight (HeIff, 1928) , molt cycle (Thompson and Pritchard, 1969) and previous activity levels (Nimura and Inoue, 1969). Relatively few investigators have examined the metabolic response of aquatic animals to wide ranges of oxygen concentration following periods of oxygen de privation. Instead, most investigations have cluaracterized the respomuse to anoxia omily at oxygen concemutratiomus at or muear air saturation. Prosser, Barr, Pinc amid Lauer (1957) luave sluowmu that golduishurespond to chronic exposure to low oxygemu cotuditiomus by a reduction of standard nuefabohism amida shuiftof critical p02 to lower oxygen partial pressures, accompamuiedby increased hemoglobin concentrations and red blood cell counts. After oxygemulack, oxygemuconsumiuptiomi rates iii tlue mwl snail NOSSOY1ZIS Ol)SOlet,lS imicrease ( Kushimus and Niangunu, 1971 ) , but the response