HETEROTHEFMY IN HOMEOTHEPMS 



IRVING: Yes, it has less significance, because it conceals 

 or disregards the physiologically important and interesting things, 

 which are the variability in temperature and circulation of the 

 different areas. 



MORRISON: Well, would you then say that the high levels of 

 hemoglobin in a diving animal are of no significance in the prolonga- 

 tion of diving, because they would not allow anything like the 

 observed increases in diving time and because the circulatory 

 changes are so much more important?Is there not an analogy here? 



IRVING: No, I would not say that the oxygen capacity of the 

 blood is unimportant for the seals. It is very important. It is not 

 the large factor in the prolongation of their dives, but presumably 

 if the blood has twice the oxygen capacity it has at least doubled 

 the transport capacity and the rate of recovery. If you get double 

 the oxygen capacity and improve the elasticity of the whole vascu- 

 lar system, then recovery is apparently attributed to those factors. 

 One of the remarkable things about such diving animals, incidentally, 

 is not only the prolonged divingbut also the rapidity with which they 

 can recover and take another dive. 



MORRISON: But when we have a factor that is advantageous, 

 when are we to say that it no longer has any significance as long 

 as it is in the right direction? Can we not say that it may have 

 selective significance, even if it is only at the 10% or 5% level? 



IRVING: Then you get one of these instances of statistical 

 significance. You are talking about imperceptible adaptations 

 which gradually accumulate by some statistical process to become 

 of visible importance. 



JOHANSEN: If you go back to heterothermy, the point here is 

 that these extremities provide insulation, and if they are larger 

 they provide more insulation. 



MORRISON: If you do not have extremities, insulation (=l/ 

 conductance) is better. 



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