[Change in the ultrastructural organization of Chaetogaster lymnaei neurons in the transition to the parasitic form of life].

The fine structure of the brain and ventral nerve cord ganglia neurons has been studied in two subspecies of Chaetogaster lymnaei, one of them being a commensal and the other the kidney endoparasite. The nerve cells of parasitic forms are characterised by the presence of a whole set of structural simplifications. These are the poorer development of endoplasmic reticulum, the greater number of free ribosomes in the cell and the less number of mitochondria with certain alternations in the ultrastructure. The given features are suggested as criteria when studying the influence of parasitic mode of life upon the ultrastructural organization of the cells.