An even more important consideration is that while 

 a pneumatophore at one atmosphere need produce only 

 enough gas to fill its observed volume, at daytime scatter- 

 ing-layer depths it will be required to produce 30 to 40 

 times its apparent volume in order to counter the collapsing 

 forces of hydrostatic pressure. Under such circumstances, 

 the observed rate of CO production is entirely too slow. 

 The probable reason for this is the nonavailability of suf- 

 ficient substrate for gas secretion, unless rate of secretion 

 varies in response to hydrostatic pressure. But even as 

 early as 1861, Keferstein and Ehlers 14 observed that filling 

 of the float was accomplished rapidly in only a few minutes. 

 This observation has been confirmed from time to time by 

 later workers. 5 



It is also possible that the automatized pneumato- 

 phores are in a more or less declining condition from the 

 moment they are brought on board thus possibly accounting 

 for the apparent lack of correlation between respiration and 

 temperature. This moribund condition could account as 

 well for some of the variability in rate of oxygen consump- 

 tion (table 1), even though care was taken to use only those 

 individuals appearing in best condition. In this context, 

 however, it is important to note that the float under discus- 

 sion, regardless of condition, did certainly produce gas, 

 and at the same time consumed oxygen at about twice the 

 rate obtained for any other float observed (table 1). This 

 single observation suggests that production of CO may in 

 fact be an aerobic and energy-requiring process, and there- 

 fore very likely does involve an enzymatic pathway, as 

 Wittenberg 16 ' 17 has indicated is the probable situation in 

 Physa^ia. Without further confirmatory data, however, 

 such a conclusion can be regarded as only tentative. 



Diffusion of Gases Across the Float Walls 



Diffusive loss of float gases can have important 

 consequences upon the buoyancy of the siphonophore colony, 

 and upon the rates of gas secretion necessary to maintain 

 buoyancy and counter ambient pressures. 



22 



