This figure should be rotated 90 degrees to the 



Igfll. Figure 4. Two living specimens of Rhizophysa sp. 



with stolon and tentacles extended. Volume of pneu- 

 matophores was 30 to 40 cubic millimeters. Distance 

 between lines on cylinder equals 1.9 mm. 



Respiratory Metabolism of Siphonopheres 



In dealing with gas and bubble production by deep-sea 

 siphonophores, rate of oxygen consumption becomes impor- 

 tant for several reasons. First, it provides an index by 

 which an estimate of presumably available aerobic energy- 

 can be made. This in turn can be compared to calculated 

 physical (but not chemical) energy requirements for main- 

 taining an inflated gas -filled float against existing hydro- 

 static pressures. Second, rate of oxygen consumption 

 appears to be correlated with the act of secretion of carbon 

 monoxide gas (see discussion below), and thus may be em- 

 ployed as a convenient analytical tool for the study of the 

 chemical reactions involved (for example, the effects of 

 various substrates or inhibitors). Third, rates of oxygen 

 consumption are an index of metabolic level, and are there- 

 fore of fundamental value in comparative physiological 

 studies of deep-sea organisms and their environmental 

 relationships (e.g., effects of pressure, and ambient 

 oxygen). 



