Abstract
The a-, t- and KRE-endosymbionts o Euscelis plebejus F. were examined by electron microscopy. They existed in two different substructural forms : a specific infectious stage I2 with double membranes, dense matrix, diffuse DNA, mesosomes, membrane stacks (a), many different inclusions, and an abundance of ribosomes, and a specific vegetative stage V2 with triple membranes (a, t), transparent matrix, possible condensed DNA, vacuoles (a), glycogen inclusions, few ribosomes and inclusions. Fine structural intermediates between these two forms existed in the "infectious" I1 and the "vegetative" V1 division stages.In view of the vast number of its organelles and the possibly less diffuse arrangement of the DNA, the infectious stage appears to be physiologically more active than the vegetative stage. In addition, they probably used different metabolic pathways.The occurrence of the stages I1, I2, V1, V2 relative to the reproductive cycles of a, t and KRE was described.The infectious and the vegetative stages were compared with the corresponding stages of ther intracellular prokaryotes such as mycoplasma and rickettsia.
