A STUDY OF THE CHROMOSOMES IN TWO SPECIES OF BATS (CHIROPTERA)

¹ Zoological Institute, Faculty of Science, Hokkaido University, Sapporo

The chromosomes of Pteropus dasymallus inopinatus, a species of the Macrochiroptera, were investigated in male germ cells. This species was found to possess the diploid number of 38 in spermatogonia and the haploid number of 19 in both of the primary and secondary spermatocytes. The karyotype of this form is noticeable in having an archaic constitution in comparison with that of other forms of mammals. Excepting a pair of elongated rod-shaped elements and a very minute Y chromosome, the remaining members of the diploid complex are all provided with atelomitic fibre attachment; the majority are J- or V-shaped. The sex chromosome mechanism was shown to be of the usual XY type. The X is represented by one of the barge J-shaped elements, consisting of two arms of very unequal length, while the Y is a minute dot, the smallest of all. At meiosis the Y is found conjugated with the X at the free end of its longer arm. In the first division the X and the Y pass to opposite poles. There result two kinds of secondary spermatocytes, one with an X and the other with the Y.

Observations upon the primary spermatocyte chromosomes reveal that Rhinolophus ferrum-equinum nippon possesses a haploid number of 29. From this haploid number it may be assumed that the diploid number of this species is 58. Judging from the configuration of the bivalents, this complement comprises both telomitic and atelomitic members. A heteromorphic XY bivalent is very distinct in the haploid group. It consists of a larger rod-shaped component, the X, and a minute dot-like one, the Y, connected end to end. They segregate in the first division.