Interrelationships between Aquatic Organisms 

 Mediated by External Metabolites 



C. E. LUCAS 



Marine Laboratory, Aberdeen, Scotland 



SEVERAL times since 1938 I have tried to review the progress 

 made in this difficult field and feel all too incompetent to do so 

 again in view of the number of those now working on one or another 

 aspect of the subject. They now represent quite a formidable 

 bibliography which provides a measure of the rate at which progress 

 is being made. 



Among those who anticipated the significance of such matters 

 were Johnstone et al. (1924), Allee (1931), Bigelow (1931), Hardy 

 (1935), and Russell (1936) and, however far we may yet have to 

 go, their prevision has in one way or another already been amply 

 justified. It was, in fact, owing to the inspiration provided by Sir 

 Alister Hardy, when he was working on his theory of animal 

 exclusion, that my interest was led toward what I called "non- 

 predatory" relationships in ecology. I hope I may be forgiven if I 

 try to look at some of the more recent progress in the light of 

 these early thoughts. I do this the less reluctantly because of the 

 comparative isolation in which the several workers on one aspect 

 or another of this problem are still working. Yet this is essentially 

 a field in which each worker needs to be in the closest touch with 

 the findings — and above all with the thoughts — of all others 

 working in it. We must therefore be particularly grateful to the 

 organizers of this meeting, who have been successful in bringing 

 together workers from Japan and Russia, from Canada and 

 Scandinavia, from the United States and the United Kingdom, to 

 exchange not only their results but their ideas. 



In essence, the earlier thesis drew attention to the general 



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