EN
The author discusses the criterion of metabolism for the differentiation of the basic relationship between two diffrent species, i. e., symbiosis, parasitism and comensalism (Smith, 1962). These considerations suggest that the criterion of metabolic dependence on the part of parasite in relation to its host, as compared with the criterion of harmfulness, gives a more satisfactory reflection of the nature and variability of interaction between the two partners, being more accurate and readily applicable to parasites, in the present state of our knowlege. On the other hand, the present knowledge of metabolism and its requirements in some interparasitic dependence forms other than parasitism (for instance in some cases of inquilism and symphilia) does not permit so far the application of the criterion of metabolic dependence. Whereever possible the application of a new criterion will often require the reclassification of some known instances of relationship between different species. There remain still the cases of trophobiosis which does not fit to Smyth's scheme. For this reason the author proposes that the notion of symbiosis given by Smith be modified in that the mutual relationship should exhibit a metabolic dependence, at least in one of the partners.