Respiration and Metabolism 



251 



of "Auznutzung" of Winterstein-"-0 under normal oxygen tensions, in lieu 

 of any wealth of information on measurements at minimum partial pressures 

 (Table 44). Although much variation prevails, certain trends among groups 

 are apparent. Withdrawal is low in the sponges, pelecypods, and ascidians, and 

 highest among the molluscs and fish. Oxygen extraction here seems to indicate 

 an improved type of respiratory mechanism. Some hesitancy should be shown 

 in accepting these figures as an over-all measure of respiratory efficiency, 

 however, as the oxygen "utilization" by definition is based solely on the per- 

 centaoe removal of oxyi>,en from the water passing across the respiratory 

 surfaces and rexeals nothing concerning the important factors of quantity 

 and rate of water pumped. For comparative purposes the withdrawal of several 



TABLE 44. OXYGEN WITHDRAWAL BY SOME AQUATIC ANIMALS 

 (Per cent O- removed from incoming water) 



