One specimen of the Japanese raccoon dog (Nyctereutesprocyonoides viverrinus) collected from Aichi-ken, Japan, has a new Robertsonian fission of the no. 6 chromosome. By the fission the basic chromosome number of this specimen is 2n=39. This specimen is also characterized by having one, two and three B-chromosomes in the somatic cells. Most of cells have two (52.4%) and three B's (45.9%). By the Robertsonian fission and B-chromosomes, this specimen is mosaic due to mainly two cell types with 41 (39+2Bs') and 42 chromosomes (39+3B's).
A male Japanese raccoon dog (Nyctereutes procyonoidesviverrinus) collected from Kanagawa-ken is remarkable for having the Robertsonian fission of three chromosomes, nos. 5, 8 and 11. By such a fission these chromosome pairs are heteromorphic in respect to two acrocentrics and one metacentric. The karyotype of this specimen is also characterized by having two to four B-chromosomes. Most cells have 3 B's (59.6%) and 4 B's (36.1%). By such a variation of B's, this specimen is to be mosaic consisting of mainly two cell types; 2n=44 chromosomes (39 autosomes+XY+3 B's) and 2n=45 (39 autosomes+XY+4 B's).
Karyotypes and distribution of B-chromosomes in four youngs from one litter are examined. They have the same basic karyotype with 2n=38. The Robertsonian fission is not observed in these specimens. Among four specimens, two specimens, RD-8404 (_??_) and RD-8406 (_??_), have the modal number of 2 B's, but the other two, RD-8405 (_??_) and RD-8407 (_??_), show to have 3 B's. The somatic variation of the number of B's is observed in these four specimens, but is slightly different from each other. The difference of the number of B's in these specimens is suggested to be due to the random distribution of B's in meiosis of the parents.
Distribution of B-chromosomes and the frequency of specimens with the Robertsonian fission are observed in 13 Japanese raccoon dogs collected in different localities. Among 13 specimens, 2 B's and 3 B's are observed in 5 specimens, respectively, and the remaining 4 specimens have 4 B's. The specimens without B's have not been observed so far. Among these animals, 5 specimens have the Robertsonian fission; three in no. 8, one in no. 6 and the remaining one in nos. 5, 8 and 11. The somatic variation of B's is analysed in 1, 372 cells in total obtained from the 13 specimens. Cells with 2, 3 and 4 B's are observed more frequently, while the cells with 1, 5, 6, and 7 B's are extremely fewer. The cells without the B's and with more than the 8 B's have not been observed. These investigations suggest that the Japanese raccoon dogs with few B-chromosomes are preferentially selected in the natural population of Japan.
The diploid chromosome numbers and karyotypes of Pracambarus clarkii and Nephrops japonicus are described by an air-drying method. The diploid chromosome number of P. clarkii is one hundred and eighty-eight (2n=188) in both the male and the female, among which forty-two meta- and submetacentric and fifty-two subtelo- and acrocentric pairs are included. The diploid chromosome number of N. japonicus is one hundred and thirty-six (2n=136) in both the male and the female, among which forty-six meta- and submetacentric and twenty-two subtelo- and acrocentric pairs are included. One subtelocentric pair of N. japonicus is remarkably large as compared with other pairs. The large chromosome pair is not found in P. clakii.