А comparative study of pretarsal modifications of approximately 350 supraspecific taxa of feather mites and representatives of ovet 50 genera of non-feather mites is presented; inter- and intragroup comparisons are made. А hypothetical pretarsus is developed and two major lines of ambulacral types are suggested; these lines indicate that certain historical divisions of the parasitic Astigmata based оп host preferences need re-examination.