Abstract
Chromosomes of the field mice, Apodemus speciosus speciosus and Apodemus speciosus ainu were studied on the basis of direct preparations from bone marrow and testis, and fetal tissues.
The basic diploid number of 48 was determined in 49 specimens of two subspecies. Two males from Gifu had 46 chromosomes. The change of the chromosome number is explicable on the basis of centric fusion known as the Robertsonian system.
