512 CYCLES OF ORC.AMC AXU INORGANIC SUBSTANCES 



appreciate the part played by smell (or taste?) in the lives of most 

 animals. Another \ ery relevant example is the observ'ed avoiding 

 reaction of Pacific salmon to the extracts of mammalian skin at 

 concentrations of only 1 X 10~' or less (Alderdyce et al., 1954). 

 Even though "ectocrine" may not be the most suitable word with 

 which to label such processes, they do appear to come within the 

 category of reactions mediated by external metabolites. 



These, then, are a few of the lines along which useful progress 

 may be made. They are not likeh* to pro\'e the best, for each year 

 we get fresh clues. Each presupposes the adaptation of organisms 

 to the environmental modifications produced by the free metabo- 

 lites of others, whether on the large or the small scale, which I 

 came to view as a key feature of ecology, as of evolution itself, 

 and a feature of terrestrial ecology in some respects no less than 

 aquatic ecology. And here, perhaps, I may beg to differ from Dr. 

 Buzzatti Traverso (1958, p. 619) in the remarks which followed 

 his very kind reference to my ideas when concluding the con- 

 ference on "Perspectives in Marine Biology" at La Jolla in 1956. 

 Then he said "It may perhaps turn out that the main difference 

 between marine and terrestrial living form lies in the requirement 

 by the former of metabolites." But, at least at the microlevel, 

 examples of such dependence can also be found on land (e.g., sex 

 processes, for which microaquatic niches of one kind or another 

 have been maintained or adapted, and, in the free air, smells 

 mediating essential processes or habits). Nor must we forget the 

 large-scale instances of ecological organization mediated by the 

 release of metabolic by-products such as oxygen and carbon 

 dioxide. They "condition" the existence of life on earth and must 

 have conditioned its evolution, on land as well as in water (see, 

 for example, Xursall, 1959). 



If this talk serves no other purpose, it may of itself perhaps 

 serve as a practical demonstration of one last aspect of the thesis 

 with which I have been and am concerned: that the release of 

 metabolites has been an important factor in mediating inter- 

 relationships within the community. In this special instance, the 

 excretion of "waste" carbon dioxide by a higher animal while 



