In order to explain several discrepancies between the gene-recombination phenomena in phages and in higher organisms, we assume that theT 2 phage, after entering the bacterium, divides in three parts corresponding to the three “chromosomes' whichHershey andRotman have traced in this phage. The three parts are supposed to be able to divide further by rupture or by the action of other “chromosome fragments”. Each fragment is supposed able to reproduce inside the bacterium as a more or less independent unit and (...) before lysis of the bacterium the various parts are assumed to reunite in complete sets of genes each forming a new phage.After discussing the experimental facts supporting these assumptions, we show that the assumptions are in perfect agreement with the theory of the symbiosis of genes, a theory which seems necessary in order to explain the ability of the “chromosome-fragments” to reunite into complete phages.Also the problems arising with respect to the sexual reproduction in bacteria is discussed under the point of view of the symbiosis theory. The assumption is made that the hereditary material is transduced from bacterium to bacterium by ultramicroscopic virus-like particles “genophores”. In several lysogenic bacteria the genophores are supposed still able to act as parasites instead of symbiontes towards some other sensitive bacteria. The experimental facts supporting this assumption are analyzed, and new experimental tests suggested. (shrink)