On the classification of the drift of the blackflies (Diptera : Simuliidae).

As to hitherto literature, there exists neither an exact characterisation n or an uniform definition for the various types of organismic drift in runni ng waters. Especially, this holds true for the terms 'catastrophic drift' a nd 'behavioural drift' which, because of their infered meaning, are critica lly re-evaluated. The abolition of this terminology is put forward. With bi ological, ethological and ecological considerations in mind, it is here sug gested that within the phenomenon drift one must distinguish between '(perm anent) dispersion' and '(aperiodic) translocation'. The basic meaning of a stringent terminology and the definition of terms concerning the drift comp lex are explained in detail for an intra- and interspecific structural anal ysis of drifting organisms in running water.