In this paper the distinguishing cytological characters, including chromosome number, karyotype and sex chromosomes, especially their size, shape and type of conjugation in meiosis, have been reviewed, based on the author's own data in 49 species of Asiatic mammals representing eight eutherian orders. The results are summarized in Table 1.
The cytological data now at hand seem not to permit any conclusion as to the evolution of karyotype in mammals. The numerical as well as morphological diversities of chromosomes in mamals are very wide, and at present our knowledge of the mammalian chromosomes is still too scanty to warrant any generalizing remarks, regarding the basal or fundamental chromosome number, or the evolutional change of karyotype.
The species here under study uniformly show the sex chromosome mechanism of the XY type in the male. Striking variations occur in size and shape of both the X and Y chromosomes from species to species. Special cyto-taxonomic interest attaches to the type of conjugation occurring between the X and Y and the mode of their segregation in meiosis; they also vary by species, but appear on the basis of present study to provide interesting cyto-taxonomic characters.