A comparative description is given of different connective tissue cells and the character of intercellular substance in the parenchyma of two species of cestodes of the order Pseudophyllidea and 4 species of the order Cyclophyllidea. The parenchyma of the cestodes has been shown to be a complex specialized tissue system evolving divergently. The first distinct morphological differences arise at the family level. The direction of the divergent evolution of the parenchyma depends on the development of certain components of intercellular substance, frequencies of individual types of cells and appearance of specific cellular element in it.