This study completes the series of morphological investigations of the main distant receptor organ in the ticks of the family Argasidae by scanning and transmitting electron microscopy and considers descriptions of the fine structure of Haller''s organs of ornithodoid (O. moubata) and otobiinoid (A. lahorensis) types. The data on Haller''s organ in argasids indicates possible ways of evolution of this organ. An important role of transformations of different nonsensory structures in the evolution was shown. Characteristic features of the evolution of the organ in argasids are: morphologically progressive differentiation of a capsule (olfactory part of the organ) and reduction of an anterior group of sensilla.