Many earlier authors have observed autologous erythrocyte-rosette formation within reddish haemolymph nodes but how and why these are formed has not been studied. In this study we traced the histogenesis of this phenomenon. Since macrophage-erythrocyte-rosettes (MER) mostly occur in the deep sinus we suggest that changes in the red blood cells caused by stagnation, aging or the loss of viability due to deoxygenation may result in development of some unusual sites on these cells. Polar formation of macrophage processes around each rosette erythrocyte in-vivo suggests loss of self-tolerance.