252 



Comparative Animal Physiology 



TABLE 44 (continued). 



OXYGEN WITHDRAWAL BY SOME AQUATIC ANIMALS 



(Per cent Oj removed from incoming water) 



air-breathers may be noted: sloth, 2 per cent; man, 4.5 per cent; porpoise, 10 

 per cent.^**''' ^^^ 



The extraction of oxygen during changes in tension may be variable; in the 

 puffer fish it remains the same over a five-fold decrease in tension, indicating 

 that the gills are equally efficient over the entire range, although they are not 

 able to make up for the lost pressure (Table 45). Furthermore, in this fish 

 withdrawal is not changed through a temperature range of 12 to 22° C.^^'^ 

 One might expect a really efficient respiratory mechanism to increase utiliza- 

 tion at lower tensions, thereby contributing to a constant oxygen consumption 

 and respiratory regulation. Crayfish--** react even less favorably to decreased 

 oxygen concentration, the extraction falling from 70 per cent at a tension of 

 160 mm. 1 Ig to 59 per cent at 50 mm. Hg. Octopus, on the other hand, as seen 

 in the table, has a higher oxygen withdrawal at the lower tensions. 



Adaptations to Low Oxygen Supply. Throughout this chapter we have 

 noted significant structural and physiological adaptations which have arisen 

 to provide oxygen for the organism, particularly under conditions of stress. 

 Scores of comparable adjustments might be enumerated, ranging from the 

 plastron mechanism of air storage in diving beetles (p. 223) to the hypertro- 

 phied gills in Sulmnandra larvae raised in oxygen-deficient water (p. 216). 



A scries o{ adaptations to oxygen lack may be considered "migratory" in 

 nature, i.e., taxic responses. The annelid worm, Tiihifex, forsakes its oozy 



