ILLUSTRATIONS 



Figure P^ge 



Frontispiece. --Transferring bait from a skiff to the bait tank of the Charles H. Gilbert . 



1 . Holding box for iao at the main laboratory 3 



2a. Diagram of the apparatus used for measuring rate of oxygen consumption 



in iao ^ 



2b. Assembly used for obtaining different temperature levels 6 



2c. Diagrann of the experimental container used in the flow rate experiments. . 6 



3. Rate of oxygen consumption (cc. /gm. /hr. ) in iao over a 24-hour period. . . 8 



4. Rate of oxygen consumption (cc. /gm. /hr. ) at different temperatures. ... 8 



5. Rate of oxygen consumption (cc. /gm. /hr. ) in iao at different rates of 



flow (liters /hour) 9 



6. Results of a field experiment testing the influence of flow rate (gal. /min. ) 



on rate of oxygen consumption (cc. /gm. /hr. ) 11 



7. Apparatus used in measuring oxygen consumption and breathing rate at 



different oxygen concentrations 14 



8. Change in rate of oxygen consumption (cc. /gm. /hr. ) with a decrease in 



the oxygen content of the water. 16 



9. Breathing rates (beats /minute) at different oxygen concentrations 16 



10. Lethal values of oxygen for iao 21 



1 1, Frequency distribution of winter lethal values of oxygen for iao 21 



12. Lethal values of oxygen at different temperatures, 24 



