RESPIRATION 153 



TABLE 4.3 — Oxygen Consumption of Some Marine Poikilotherms (continued) 



A variable proportion of dry weight consists of inactive material, 

 chitin, skeleton, etc. In a detailed study Zeuthen (171) has related the 

 oxygen consumption of many marine animals to N-content, and his results 

 are summarized in Fig. 4.8. On this basis the metabolism of lower inverte- 

 brate animals of comparable size (coelenterates, echinoderms, worms, 

 gastropods) shows much correspondence. The curve for Mytilus reveals 

 very low values, perhaps correlated with its sedentary habits. Moreover, 

 there is indication of increased respiratory rate per unit-N in animals 

 higher up in the phyletic scale, namely crustaceans and fish. These are 

 also more active than the invertebrates previously mentioned, but in 

 addition there appears to be a real difference related to higher metabolism 

 in the more advanced phyla. 



Effect of Size. It has long been recognized that rates of oxygen con- 

 sumption are generally lower in larger animals of the same or closely 

 related species. Earlier data are inconsistent, but more recent studies on a 

 wide variety of animals have confirmed this inverse relationship between 

 metabolic rate and body size. The relationship is not linear; rather the 



