SUMMARY
The chromosomes of the following pikas (Ochotona) are described: O. pusilla, 2n = 68; O. rutila and O. macrotis, 2n = 62; O. rufescens, 2n = 60; O. daurica, 2n = 50; O. alpina, 2n=42; O. hyperborea, 2n = 40; O. pricei, 2n = 38. O. alpina and O. hyperborea are proved to be independent species.
It is shown that O. hyperborea from Northern Ural, Magadan and Hokkaido; O. pricei from Central Kazakhstan and Altai; O. daurica from Altai and Transbaikal are indistinguishable in karyotypes. The palaeogeographic disjunction of the ranges of the pikas date from the Kargin interglacial period. The time period encompassing 30,000 generations is not considered sufficient for the establishment of cytologically differentiated sibling species. The penetration of Ochotona into North America has possibly occured as early as the Eupleistocene.